I have a PC that is about 3 years old, running Windows 10 Home 64 Bit. Starting sometime in late Oct it started randomly accessing (drives/CPU/?) every so often, causing significant stuttering and making it generally unusable for a few minutes at a time until it is done. It does this once every 45-90 minutes, fairly reliably. Recently it has occasionally (once every day or two) set off a longer cycle of the same symptoms that forces me to either wait much longer (hours) or reboot if I want to get back to normal.
I did some cursory poking around, and it turns out that every time this happens, Windows Security is doing a Device Performance & Health Scan. (Not a threat or security scan; the Device Performance and Health tab only is updated, the Last Scan date and time.) When the "longer" variety occurs, it's running non-stop back-to-back Health Scans. Either something is causing Windows Security to do the Health Scan far more often than it should and that is causing the performance issue, or something unrelated is going wrong that is causing Windows Security to do the Health Scan as a result. The Health Report is green across the board and there are no obvious system issues, and I have had no other major problems for the life of this computer. No hardware or usage pattern changes. Looking at my update history, this would have started around the time that I installed the 2020-10 Cumulative Update (KB4578311); I have since installed the 2020-11 and -12 updates and am currently fully up to date on all Windows Updates.
My next step would normally be to turn off the Device Performance & Health Scan function to see whether that's the cause or the effect, but it doesn't look like I can do that without getting rid of Windows Security entirely (and maybe not even then?). I am generally tech-savvy but I have limited experience in digging too deep into the Windows troubleshooting tools. I'd really prefer not to do a fresh install without at least identifying the problem first (if only to make sure it's not hardware related or some unknown driver conflict). Thoughts on where I should be looking to hunt this down, or any other suggestions? I appreciate the assistance!