Since my OP I’ve tried a number of additional “fixes” to resolve the 100% system disk activity problem. None of them has worked for me. But all of them have worked for other people, so they might work for you if you have this problem. Currently I’m downloading a Win10 iso image to do a clean install.
Here’s the other things I’ve tried:
- Disabled prefetch using regedit
- Disabled all Windows notifications using Settings
- Updated the firmware on the SSD used as a system disk
- Disabled Windows Search in Computer Managment/Services (type “services” in Start Menu)
- Disabled Background Intelligent Transfer in Computer Managment/Services