I wish to retract my original post- although I don't think the TiVo server was supposed to be enabled, it no longer appears to have been solely responsible for my problem.
While writing this thread, I think I diagnosed the problem, so am going to post this in case anyone else runs into this particularly weird and vexing problem:
TLDR: The (completely unused) TiVo Server module was causing crippling CPU spikes.
Longer writeup:
Sometime in the last month, I have started to experience Windows system hangs that would always get progressively more severe until the system became unusable. Through a bunch of diagnosis, I was able to narrow down the culprit to Media Center. I turned on MC logging and monitored the log in realtime while watching Performance Monitor for MC CPU spikes and it looks like they always correspond with a series of TV: CTVManager operations.
Here's a relevant section:
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Red (Generic DLNA) not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Red (Audiophile 24-bit DAC) not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Red (Library Server) not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Red not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: DP-UB420 not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Family Room not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Family Room not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Network Camera Front Window not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Family Room not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: GS908E (CC:40:D0:39:46:02) not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: RED: RED: not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: DCS-936L-Driveway (192.168.0.248) not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: DP-UB420 not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Christmas Tree not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Grandfather Clock not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Study Room 4K FireTV Stick not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Lori's Fire TV not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: TCL Roku TV not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
1512047: 15828: Sharing Plugins: CMCDLNA::DLNACore_DevicesChanged: Checking TV devices. TVManager 0x24fbcb775a0
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Start
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Front Porch not TV device
1512047: 15828: TV: CTVManager::AddDLNATVDevice: Finish (0 ms)
I had attempted a whole host of troubleshooting steps, including uninstalling and reinstalling + removing all the DLNA types and turned off all but the core audio and video playback features. I was surprised when I saw TV: CTVManager show up as a corresponding event in the log because I had turned off the TV feature as part of troubleshooting. So I went hunting for any remaining services that seemed possibly related and found the TiVo Server, which I'd never touched, listed under Services. It wasn't active, but I removed the interface anyways and I haven't had a single CPU spike since then.
I searched Interact for information on the TiVo Server and could only find really old threads with broken links. Is TiVo even a currently supported thing or did I have some old vestigial remnant of upgrading all these years? I can't even find a way to get it back, not that I'd want to.[/s]