Three weeks ago I had an issue with MS Office 2013 on my Dell (Win 10) that necessitated their support guy to take control of my PC and make the fix (I have a four year warranty with support). While trying to make the fix, he commented that my machine was very slow for an i7 processor (like taking ten minutes for a reboot!) and that he suspected malware. He ran Malwarebytes with no luck, and tried a few other things (which I didn't understand). Eventually, he asked me to back up my settings and data, and said he'd call me the next day to do a clean install of 8.1 and clean upgrade to 10.

The clean installs went fine, and I spent the next couple of evenings reloading my settings and data, and re-installing my other software...MS Office 2013, Reaper, Audacity, Photoshop, yadda yadda. The result is a PC that runs like lightning, and everything is working exactly as it should.

During our conversations the Dell guy told me that they do not recommend the standard upgrade, which often results in the kinds of problems that people are relating above, but that they always recommend a clean upgrade, which invariably produces good results.

Scary stuff, but well worth the effort, AFAIC.