Thanks, I'll look at that link!
Nvidia, yes, I tend to install only the necessary drivers and no extra bloatware, same goes for HP and other usual offenders
MIDI is part of the UA25EX, and used to work, including in Reaper, on that windows installation, but with older mainboard.
I would guess that this is now in a USB3 port than the USB2 before, and I don't have the panel connectors for USB2 interior sockets yet (my case is apparently also a bit on the older side, the connectors don't match).
If maybe the UA25EX is not 100% standards compliant and something in the maybe stricter backwards compatibility of the USB3 rubs against that, perhaps something roughly like that causes this problem... *wild guess* But maybe I'll reinstall the drivers for the whole thing.
But let's wait what happens when the USB2 connectors have arrived.
I will post what did the trick if it resolved.