Another thing I noticed now regarding this issue is that if you have too many incorrect attempts on one of the profiles with the fingerprint, then the fingerprint also gets disabled in the other profile (change profile through lockscreen) and it asks for pw there too. Once pw is is entered the fingerprint starts to work again.
So somehow it seems some information regarding fingerprint configuration/settings or something else is shared among profiles hence the limit and workaround regarding the 2+2 fingers.
If this helps any DEV.