Hello and welcome to the forum 
How long have you been using krita?
I ask because krita does not have an eraser tool and you may not be aware of how the ‘pen tip’ and the ‘eraser tip’ are treated/interpreted within krita.
Essentially, they are treated as ‘tip-A’ and ‘tip-B’ and each of them can be used, independently, to select any brush preset for use. Which brush tip is selected and used at each end is up to you to decide and will be remembered during the session.
So, if you use the ‘pen tip’ to select e.g. Bristles-Flat-Rough, you’ll paint with that.
If you then use the ‘eraser tip’ to select e.g. Eraser Circle, you’ll paint with that - and Eraser Circle is an erasing brush preset so you’ll have an erasing effect when you use the ‘eraser tip’.
Treat them as two separate painting tips (A and B) instead of painting vs erasing functions.
Also, if you lift the pen from the tablet while using the tablet tester, then bring it close again, the right side record will tell you if it’s detected as a ‘pen’ or an ‘eraser’ tip.