Facetime Audio call from iPhone - Bizarre problem

I Have a bizarre problem with FaceTime Audio on my iPhone17 pro.

IOS 26 latest updates etc.

When I start a FaceTime audio call, the phone makes the usual ringing noise.

Roughly 1 in 3 calls have the following problem:

Other party answers, and we can talk to each other but the ringing continues.

There is no way to end the call. Pressing the end call button does nothing, either before the other party answers or during the call.

The only way out of this knot is hard reset of the iPhone.

Anybody else seen this or got any ideas ? It' driving me crazy. It's only been happening since I updated to IOS 26