After further testing today another problem, probably related. Waiting on tech support response.
I have tested further and now when the phone rings and I answer on the
3rd or 4th ring it disconnects the call. If I immediately call back
and try again it will ring and then can allow it ring 3 times and
answer and it connects.
When this happens if I successfully talk then hang up, and another
call rings within a short time (less than about 5 min) then the phone
can ring and answer on the 3rd or 4th ring. However, after this few
minutes between calls and I allow the phone to ring 3 or 4 times, it
happens again and disconnects the call.