Upon further testing:
Just playing music works fine, no excess ram/swap usage. So, I decided to test the Analyze Audio function.
I've rebooted the mini, launched MC, opened the Analyze Audio window and left it to work on the rest of my collection - I watched it for a while and it seemed to eat up the "Cached Files" part of memory right up until it hit 16GB (total, combined with "Used Memory") and then it went into swap (that was after about 100-200 files scanned).
I left it there to do its thing and came back after an hour or so... to a rebooted system
It managed to chew trough another ~800-1000 files it seems before the whole thing crashed (looking at the number still left to scan).
It looks to me like it's some kind of memory management issue, not sure if on JRiver part or MacOS but that kind of behavior cannot be normal?
EDIT: also, exiting MC does not free up the swap/cached files part of memory. So doing the analysis in chunks would require rebooting in between it seems.
EDIT 2: Here's the crash report.
panic(cpu 1 caller 0xfffffe002a1f5e58): userspace watchdog timeout: no successful checkins from com.apple.WindowServer in 142 seconds
service: com.apple.logd, total successful checkins since load (1933 seconds ago): 191, last successful checkin: 0 seconds ago
service: com.apple.WindowServer, total successful checkins since load (1903 seconds ago): 176, last successful checkin: 142 seconds ago
Debugger message: panic
Memory ID: 0xff
OS release type: User
OS version: 20F71
Kernel version: Darwin Kernel Version 20.5.0: Sat May 8 05:10:31 PDT 2021; root:xnu-7195.121.3~9/RELEASE_ARM64_T8101
Fileset Kernelcache UUID: FB10CC0AB8BAC020BC47A50D64476F11
Kernel UUID: 07259C53-9EF7-32FF-821D-8F28A5985DFA
iBoot version: iBoot-6723.120.36
secure boot?: YES
Paniclog version: 13
KernelCache slide: 0x000000001f740000
KernelCache base: 0xfffffe0026744000
Kernel slide: 0x0000000020288000
Kernel text base: 0xfffffe002728c000
Kernel text exec base: 0xfffffe0027358000
mach_absolute_time: 0xae43fea33
Epoch Time: sec usec
Boot : 0x60dc8d4c 0x000d628d
Sleep : 0x00000000 0x00000000
Wake : 0x00000000 0x00000000
Calendar: 0x60dc94e2 0x000b5a7d
CORE 0 recently retired instr at 0xfffffe00274ca6f4
CORE 1 recently retired instr at 0xfffffe00274c9240
CORE 2 recently retired instr at 0xfffffe00274ca6f4
CORE 3 recently retired instr at 0xfffffe00274ca6f4
CORE 4 recently retired instr at 0xfffffe00274ca6f8
CORE 5 recently retired instr at 0xfffffe00274ca6f8
CORE 6 recently retired instr at 0xfffffe00274ca6f8
CORE 7 recently retired instr at 0xfffffe00274ca6f8
Total cpu_usage: 79198598
Thread task pri cpu_usage
0xfffffe1668dcaca0 watchdogd 97 5563
0xfffffe1666f98000 kernel_task 91 4075870
0xfffffe166a742ca0 com.apple.AppleU 63 116550
0xfffffe166f382ca0 xpcproxy 47 125532
0xfffffe166816b960 thermalmonitord 46 166270
Panicked task 0xfffffe16681747d8: 72 pages, 4 threads: pid 93: watchdogd
Panicked thread: 0xfffffe1668dcaca0, backtrace: 0xfffffe4017ceb180, tid: 1902
lr: 0xfffffe00273a6be4 fp: 0xfffffe4017ceb1f0
lr: 0xfffffe00273a69c8 fp: 0xfffffe4017ceb260
lr: 0xfffffe00274cfa70 fp: 0xfffffe4017ceb280
lr: 0xfffffe00274c12b8 fp: 0xfffffe4017ceb330
lr: 0xfffffe002735f7e8 fp: 0xfffffe4017ceb340
lr: 0xfffffe00273a6658 fp: 0xfffffe4017ceb6d0
lr: 0xfffffe00273a6658 fp: 0xfffffe4017ceb740
lr: 0xfffffe0027b5842c fp: 0xfffffe4017ceb760
lr: 0xfffffe002a1f5e58 fp: 0xfffffe4017ceb780
lr: 0xfffffe002a1f5a34 fp: 0xfffffe4017ceb7a0
lr: 0xfffffe0027ac12f0 fp: 0xfffffe4017ceb800
lr: 0xfffffe002a1f4914 fp: 0xfffffe4017ceb920
lr: 0xfffffe0027ace83c fp: 0xfffffe4017cebab0
lr: 0xfffffe0027492774 fp: 0xfffffe4017cebbd0
lr: 0xfffffe00273ac32c fp: 0xfffffe4017cebc40
lr: 0xfffffe002738399c fp: 0xfffffe4017cebcc0
lr: 0xfffffe002739c7f0 fp: 0xfffffe4017cebd70
lr: 0xfffffe00274b5c40 fp: 0xfffffe4017cebe40
lr: 0xfffffe00274c1334 fp: 0xfffffe4017cebef0
lr: 0xfffffe002735f7e8 fp: 0xfffffe4017cebf00
Kernel Extensions in backtrace:
com.apple.driver.watchdog(1.0)[D44D6C64-F220-3976-A01A-F0DC2382A908]@0xfffffe002a1f4000->0xfffffe002a1f7fff
last started kext at 774139470: com.apple.filesystems.smbfs 3.6 (addr 0xfffffe0027260000, size 65536)
loaded kexts:
com.apple.filesystems.smbfs 3.6
com.apple.filesystems.autofs 3.0
com.apple.fileutil 20.036.15
com.apple.driver.AppleALSColorSensor 1.0.0d1
com.apple.iokit.IOBluetoothSerialManager 8.0.5d7
com.apple.driver.AppleBiometricServices 1
com.apple.driver.BCMWLANFirmware4378.Hashstore 1
com.apple.driver.AppleAOPVoiceTrigger 11.5
com.apple.driver.AppleThunderboltIP 4.0.3
com.apple.iokit.AppleBCM5701Ethernet 11.0.0
com.apple.driver.CoreKDL 1
com.apple.driver.SEPHibernation 1
com.apple.driver.DiskImages.ReadWriteDiskImage 493.0.0
com.apple.driver.DiskImages.UDIFDiskImage 493.0.0
com.apple.driver.DiskImages.RAMBackingStore 493.0.0
com.apple.driver.DiskImages.FileBackingStore 493.0.0
com.apple.driver.AppleUSBDeviceNCM 5.0.0
com.apple.filesystems.apfs 1677.120.9
com.apple.driver.AppleSmartBatteryManager 161.0.0
com.apple.driver.AppleFileSystemDriver 3.0.1
com.apple.security.BootPolicy 1
com.apple.BootCache 40
com.apple.AppleFSCompression.AppleFSCompressionTypeZlib 1.0.0
com.apple.AppleFSCompression.AppleFSCompressionTypeDataless 1.0.0d1
com.apple.nke.l2tp 1.9
com.apple.filesystems.tmpfs 1
com.apple.IOTextEncryptionFamily 1.0.0
com.apple.filesystems.hfs.kext 556.100.11
com.apple.driver.ApplePMP 1
com.apple.driver.AppleSmartIO2 1
com.apple.driver.ApplePMPFirmware 1
com.apple.AppleEmbeddedSimpleSPINORFlasher 1
com.apple.driver.AppleTAS5770LAmp 442.26
com.apple.driver.AppleCS42L83Audio 442.26
com.apple.driver.AppleSPMIPMU 1.0.1
com.apple.driver.AppleT8020SOCTuner 1
com.apple.driver.AppleT8103CLPCv3 1
com.apple.driver.AppleSPIMC 1
com.apple.AGXG13G 173.28.1
com.apple.driver.AppleAVD 381
com.apple.driver.AppleAVE2 401.73.3
com.apple.driver.AppleJPEGDriver 4.6.0
com.apple.driver.AppleMobileDispH13G-DCP 140.0
com.apple.driver.usb.AppleUSBHostT8103 1
com.apple.driver.AudioDMAController-T8103 1.60.5
com.apple.driver.AppleS5L8960XNCO 1
com.apple.driver.AppleT8103PMGR 1
com.apple.driver.AppleS8000AES 1
com.apple.driver.AppleS5L8920XPWM 1.0.0d1
com.apple.driver.AppleS8000DWI 1.0.0d1
com.apple.driver.AppleS5L8960XWatchDogTimer 1
com.apple.driver.AppleInterruptController 1.0.0d1
com.apple.driver.AppleBluetoothModule 1
com.apple.driver.AppleSamsungSerial 1.0.0d1
com.apple.driver.AppleBCMWLANBusInterfacePCIe 1
com.apple.driver.AppleMCDP29XXUpdateSupport 1
com.apple.driver.AppleT8020DART 1
com.apple.driver.AppleS5L8940XI2C 1.0.0d2
com.apple.driver.AppleT8101 1
com.apple.driver.AppleM68Buttons 1.0.0d1
com.apple.iokit.IOUserEthernet 1.0.1
com.apple.driver.usb.AppleUSBUserHCI 1
com.apple.iokit.IOKitRegistryCompatibility 1
com.apple.iokit.EndpointSecurity 1
com.apple.driver.AppleDiskImages2 1
com.apple.AppleSystemPolicy 2.0.0
com.apple.nke.applicationfirewall 311
com.apple.kec.InvalidateHmac 1
com.apple.kext.triggers 1.0
com.apple.iokit.IOAVBFamily 940.4
com.apple.plugin.IOgPTPPlugin 985.2
com.apple.iokit.IOEthernetAVBController 1.1.0
com.apple.driver.AppleMesaSEPDriver 100.99
com.apple.iokit.IOBiometricFamily 1
com.apple.driver.usb.IOUSBHostHIDDevice 1.2
com.apple.driver.usb.cdc 5.0.0
com.apple.driver.AppleUSBAudio 405.39
com.apple.iokit.IOAudioFamily 300.6.1
com.apple.vecLib.kext 1.2.0
com.apple.driver.AppleAOPAudio 16.2
com.apple.driver.IOBluetoothHostControllerPCIeTransport 8.0.5d7
com.apple.iokit.IOBluetoothHostControllerTransport 8.0.5d7
com.apple.driver.usb.AppleEmbeddedUSBXHCIPCI 1
com.apple.driver.usb.AppleUSBXHCIPCI 1.2
com.apple.driver.AppleEmbeddedUSB 1
com.apple.driver.AppleConvergedIPCOLYBTControl 1
com.apple.driver.AppleConvergedPCI 1
com.apple.driver.AppleBluetoothDebug 1
com.apple.driver.AppleSEPHDCPManager 1.0.1
com.apple.driver.AppleTrustedAccessory 1
com.apple.iokit.AppleSEPGenericTransfer 1
com.apple.driver.DiskImages.KernelBacked 493.0.0
com.apple.driver.usb.networking 5.0.0
com.apple.driver.AppleThunderboltUSBDownAdapter 1.0.4
com.apple.driver.AppleThunderboltDPInAdapter 8.1.4
com.apple.driver.AppleThunderboltDPAdapterFamily 8.1.4
com.apple.driver.AppleThunderboltPCIDownAdapter 4.1.1
com.apple.driver.AppleBTM 1.0.1
com.apple.driver.AppleXsanScheme 3
com.apple.driver.AppleDCPDPTXProxy 1.0.0
com.apple.nke.ppp 1.9
com.apple.driver.DCPDPFamilyProxy 1
com.apple.driver.AppleBSDKextStarter 3
com.apple.filesystems.hfs.encodings.kext 1
com.apple.iokit.IONVMeFamily 2.1.0
com.apple.driver.AppleSPU 1
com.apple.driver.AppleHPM 3.4.4
com.apple.driver.AppleDiagnosticDataAccessReadOnly 1.0.0
com.apple.driver.AppleNANDConfigAccess 1.0.0
com.apple.AGXFirmwareKextG13GRTBuddy 173.28.1
com.apple.AGXFirmwareKextRTBuddy64 173.28.1
com.apple.driver.AppleStockholmControl 1.0.0
com.apple.driver.AppleCSEmbeddedAudio 442.26
com.apple.driver.AppleEmbeddedAudio 442.26
com.apple.iokit.AppleARMIISAudio 80.34.1
com.apple.driver.AppleDialogPMU 1.0.1
com.apple.driver.ApplePassthroughPPM 3.0
com.apple.driver.AppleMCA2-T8103 540.10
com.apple.iokit.IOGPUFamily 21.11
com.apple.driver.AppleH11ANEInterface 4.75.0
com.apple.driver.DCPAVFamilyProxy 1
com.apple.iokit.IOMobileGraphicsFamily-DCP 343.0.0
com.apple.driver.AppleDCP 1
com.apple.driver.AppleFirmwareKit 1
com.apple.iokit.IOMobileGraphicsFamily 343.0.0
com.apple.driver.AppleSPMI 1.0.1
com.apple.driver.AppleUSBXDCIARM 1.0
com.apple.driver.AppleUSBXDCI 1.0
com.apple.iokit.IOUSBDeviceFamily 2.0.0
com.apple.driver.usb.AppleUSBXHCIARM 1
com.apple.driver.usb.AppleUSBXHCI 1.2
com.apple.driver.AppleEmbeddedUSBHost 1
com.apple.driver.usb.AppleUSBHub 1.2
com.apple.driver.usb.AppleUSBHostCompositeDevice 1.2
com.apple.driver.AppleT8103TypeCPhy 1
com.apple.driver.AppleSART 1
com.apple.driver.ApplePMGR 1
com.apple.driver.watchdog 1
com.apple.driver.usb.AppleUSBHostPacketFilter 1.0
com.apple.driver.AppleDisplayCrossbar 1.0.0
com.apple.driver.AppleTypeCPhy 1
com.apple.driver.AppleThunderboltNHI 7.2.8
com.apple.driver.AppleT8103PCIeC 1
com.apple.iokit.IOThunderboltFamily 9.3.2
com.apple.driver.ApplePIODMA 1
com.apple.driver.AppleT8103PCIe 1
com.apple.driver.AppleMultiFunctionManager 1
com.apple.driver.AppleEmbeddedPCIE 1
com.apple.driver.AppleBluetoothDebugService 1
com.apple.driver.AppleBCMWLANCore 1.0.0
com.apple.iokit.IO80211FamilyV2 1200.12.2b1
com.apple.driver.IOImageLoader 1.0.0
com.apple.driver.corecapture 1.0.4
com.apple.iokit.IODisplayPortFamily 1.0.0
com.apple.driver.AppleGPIOICController 1.0.2
com.apple.driver.AppleFireStormErrorHandler 1
com.apple.driver.AppleMobileApNonce 1
com.apple.iokit.IOTimeSyncFamily 985.2
com.apple.driver.DiskImages 493.0.0
com.apple.iokit.IOGraphicsFamily 585.1
com.apple.iokit.IOBluetoothFamily 8.0.5d7
com.apple.iokit.IOBluetoothPacketLogger 8.0.5d7
com.apple.driver.FairPlayIOKit 68.7.1
com.apple.iokit.CoreAnalyticsFamily 1
com.apple.driver.AppleSSE 1.0
com.apple.driver.AppleSEPKeyStore 2
com.apple.driver.AppleUSBTDM 511.120.2
com.apple.iokit.IOUSBMassStorageDriver 184.121.1
com.apple.iokit.IOPCIFamily 2.9
com.apple.iokit.IOSCSIBlockCommandsDevice 436.121.1
com.apple.iokit.IOSCSIArchitectureModelFamily 436.121.1
com.apple.driver.AppleIPAppender 1.0
com.apple.driver.AppleFDEKeyStore 28.30
com.apple.driver.AppleEffaceableStorage 1.0
com.apple.driver.AppleCredentialManager 1.0
com.apple.driver.KernelRelayHost 1
com.apple.iokit.IOUSBHostFamily 1.2
com.apple.driver.AppleUSBHostMergeProperties 1.2
com.apple.driver.usb.AppleUSBCommon 1.0
com.apple.driver.AppleSMC 3.1.9
com.apple.driver.RTBuddy 1.0.0
com.apple.driver.AppleEmbeddedTempSensor 1.0.0
com.apple.driver.AppleARMPMU 1.0
com.apple.iokit.IOAccessoryManager 1.0.0
com.apple.driver.AppleOnboardSerial 1.0
com.apple.iokit.IOSkywalkFamily 1
com.apple.driver.mDNSOffloadUserClient 1.0.1b8
com.apple.iokit.IONetworkingFamily 3.4
com.apple.iokit.IOSerialFamily 11
com.apple.driver.AppleSEPManager 1.0.1
com.apple.driver.AppleA7IOP 1.0.2
com.apple.driver.IOSlaveProcessor 1
com.apple.driver.AppleBiometricSensor 2
com.apple.iokit.IOHIDFamily 2.0.0
com.apple.AUC 1.0
com.apple.iokit.IOAVFamily 1.0.0
com.apple.iokit.IOHDCPFamily 1.0.0
com.apple.iokit.IOCECFamily 1
com.apple.iokit.IOAudio2Family 1.0
com.apple.driver.AppleEmbeddedAudioLibs 1.17
com.apple.driver.AppleFirmwareUpdateKext 1
com.apple.driver.AppleM2ScalerCSCDriver 265.0.0
com.apple.iokit.IOSurface 290.8.1
com.apple.driver.IODARTFamily 1
com.apple.security.quarantine 4
com.apple.security.sandbox 300.0
com.apple.kext.AppleMatch 1.0.0d1
com.apple.driver.AppleMobileFileIntegrity 1.0.5
com.apple.kext.CoreTrust 1
com.apple.security.AppleImage4 3.0.0
com.apple.iokit.IOCryptoAcceleratorFamily 1.0.1
com.apple.driver.AppleARMPlatform 1.0.2
com.apple.iokit.IOStorageFamily 2.1
com.apple.iokit.IOSlowAdaptiveClockingFamily 1.0.0
com.apple.iokit.IOReportFamily 47
com.apple.kec.pthread 1
com.apple.kec.corecrypto 11.1
com.apple.kec.Libm 1
** Stackshot Succeeded ** Bytes Traced 303226 (Uncompressed 746640) **