That's weird - I'd probably start and restore all user/admin settings to factory default. And also clear the SP modes (no "clear all" of course) and...
Oops, I'd suggest to use Xampp to perform the update/migration/test - workflow on your local PC so you don't have to screw around with the live data...
Looks like HV fluctuations / issues - might be caused by worn out/defective consumables or bad contacts.
It's not unusual that one issue can sort of...