Antivirus problems with MC are common. Antivirus nowadays are more often than not 'guessing' based on application behavior than actually detecting known virus. Because MC is a complex software that accesses many files and network resources, it tends to trigger close automated scrutiny from the Antivirus, often causing slowdowns or breaking features due to the AV blocking access to some file or resource.
The common solution is to tell the AV to exclude MC from scanning. There are however different ways to do this - this post explains the differences.
CAVEAT: only do this is you really trust JRiver not to drop a BTC miner or Trojan on your machine

The best way to avoid AV problems is to exclude the MC
processes, not just the folder or EXE files. In Defender and other AVs you can add Folder/File/Extension/Process exclusions; these have different effects:
Exclusion type | Description |
Folder | Files within the folder will not be scanned when executed or accessed |
File | This single file will not be scanned when executed or accessed |
Extension | Files with this extension will not be scanned when accessed by any application |
Process | Any files opened/accessed/updated by this process will not be scanned, regardless of location |
If you add simply exclude the C:\Program Files\J River\Media Center
folder, the Antivirus will still intercept and monitor ALL files opened/created/updated by MC, and ALL network connections it does. It just won't scan the MC application files themselves.
The same applies if you simply exclude the Media Center 34.exe/JRService.exe/JRWeb.exe/JRWorker.exe
files - the EXE files themselves will not be scanned, but everything they do will still be monitored and potentially interfered with.
Excluding the
Processes of Media Center 34/JRService/JRWeb/JRWorker will actually tell the AV to ignore ALL activity performed by these applications. This ensures it won't interfere with media file accesses and network operations. Make sure to add exclusions for each of these processes as all of them perform different MC tasks.
Note that a Process exclusion in Defender doesn't exclude the actual EXE file, just its behavior - so you should still also exclude the MC Folder so that opening MC doesn't trigger a potentially fake detection on the EXE itself.