Cannot answer calls

[Sonyuser32]

Hi, I have a Sony Xperia Z5 compact.  If I recieve a call when the phone is not active, I get the normal 'swipe' to answer at the bottom of the screen, and when I swipe it works.  However if the phone is active - ie because I am looking at emails / internet etc- I get the 'floating' decline / answer at the top of the screen.  However whether I click on decline or answer nothing happens.  This means that I keep missing calls.  Any suggestions or help?  Thanks 

[_alexdon_]

Check if the same occurs in safe mode. It should reject.

[RobertoDS]

This happens also on a Moto G 2014 we've in our family, and happens sometimes ... I think it's due by Facebook