Calls – No answer screen on SIM1

My V20 has just developed a problem with incoming calls on SIM1: they sound but nothing is displayed to answer it, whether on the main screen or secondary. SIM2 seems to work correctly.

I've tried removing the Contacts cache, restarting and changing the screen for advice on incoming calls, but nothing.

Contacts> App Notifications has only two options: "On" and "Icon", both of which are enabled, which may be fine, but seems a little sparse.

I have the impression that this may have happened since I paired it with my car, but not pairing does not solve the problem, so I'm not sure that this is associated.

The problem disappears when I swap the two SIM cards but comes back when I restore them.

Anyone have any suggestions for remedying it?

Ian