So the issue is happening again, randomly. Turning the mouse to pen like above didn't help this time. I did a fresh install of 4.8.07 (Was using 4.8.04) and the issue still happened. No opacity or radius changes when pressured with my Wacom tablet.
Again, I'm running Windows 10, and reinstalling the driver / resetting the Wacom service did not help. Any ideas?
Thanks!
(The 3D-Coat pressure tester has shown me inputting pressure, and it works fine with Photoshop).