There have been a few people report a similar problem in the past. You may be able to find the threads with a search.
When you watch live TV MC plays the video using a different video engine compared to when playing a recording. So if you pause Live TV for a bit longer than 2-3 seconds, you can build up enough buffer so that MC is effectively playing a recording. Sometimes that is enough to prevent the runaway video issue.
I think previous issues were solved with things like a reinstallation of MC, as something had gotten messed up at some stage. Not something I usually advise, but doing a manual library backup, full uninstall including settings, reinstall and restore of the database including settings might fix the problem. If MC and your library are on your boot drive, it may pay to do a backup of the full boot drive before the uninstall, in case something really goes wrong.
Other less drastic things that may fix it are deleting madVR (if you use ROHQ) and the LAV subdirectories, then play video in MC to initiate the download and reinstallation of those components again.
With an HDHomeRun there have also been some reports of power supply failures, or failing power supplies, causing all sorts of trouble, such as this. So if your HDHomeRun is old, or lived in a hot environment much of the time, a new power supply might fix it. Firmware and software updates have fixed some problems for those tuners as well. Although they usually fix problems caused by Windows updates. If you have stayed on the one version of MC22 for some time, but are using Windows 10 now on your new PC, an HDHomeRun software update, which includes the firmware in most updates (check their change log as not all updates include firmware), could fix your issue.
I guess though if you only just upgraded your PC, you would have done a clean Windows 10 installation and used all the latest drivers, software, and would have a clean MC installation?