Gosh. You are right! It works properly without connected tablet! You think its problem with tablet/tablet settings?
it’s either some obscure unity input bug or I know the windows ink thing brings a lot of trouble. There’s a setting in the Wacom configuration panel to disable windows ink, i’d try that. If that and updating the Wacom drivers doesn’t solve it I’d have a hard time finding a fix for it on my end since unity doesn’t really offer any drawing tablet support I can hook on to..
Update Wacom drivers helps! (Was: 6.3.20; Now: 6.3.30-2).
By the way, seems like the Mac version doesn't have "windows ink" option. As far, as I understand, the issue with it is Windows-related.
Thank you, this is a huge relief