I don't even know how to explain this so here's a video
https://youtu.be/QMoi2bm1Yts

If you go back to using 4.2.4 (or whatever you had), does this problem still happen? You can use the standalone .zip version to bypass the need to reinstall if you prefer. Does it happen with the 4.2.6 beta?: https://krita.org/en/item/help-beta-test-krita-4-2-6/

Which tablet do you have and is there any possibility that a Windows update has affected it. Have you tried reinstalling the tablet drivers?

See also if it helps to simply switch the tablet API under Configure Krita > Tablet Settings to Windows 8+ Pointer Input (Windows Ink) and then restart Krita.