Hi! I have this problem I couldn't solve myself or find an existing forum of.
My problem is that when drawing, sometimes only the mouse works.
Sometimes, the pen somehow works but I cannot end a line, even when lifting the pen. The only way to end a line is to click the pen as if I were using it.
This leads me to belive that this is a Pen - Mouse issue.
I have tried: Updating (Tablet and Krita), restarting PC, unplugging tablet and replugging.

Using Huion Kamvas 16

Try to change the API in Configure Krita -> Tablet Settings from Wintab to Windows 8+ Pointer. If it doesn't work, you can contact Huion support service, they declare to support Krita and try to help with problems like that.