[PatK]

I then tried VLC, no issues whatso-ever

VLC is always my default looking for Kodi playback issues, it's basically the same code that is in Kodi (nice part of open source) but a step back, so from my point of view, if VLC works fine, then Kodi should work fine, although VLC is set for software default, while Kodi tries to default to hardware acceleration. I have found that MPC-HC proprietary drivers seems to play h265 more efficiently, and could be used as an external player stop gap measure until we have new code from hardware manufacturers and our team. I'm not a windows 10 user yet, so couldn't comment on your suppositions of the newly installed o/s. You might want to toggle some of the video attributes in Kodi and see if you can get VLC level of playback, and I have noticed that Krypton is slightly better at handling h265.

Season greetings.