Why does my Apple Watch Ultra 2 timer screen keep freezing?

On my ultra 2, occasionally the main timer screen will freeze in that the timer is not reducing (see screenshots)

As you will see the main countdown is frozen and yet the other screen is fine.

The timers when this happens still complete and the notification sound still plays.

This particular freeze happened today with the latest watchOS 11.4 installed... however it still happened on previous releases.

Watch gets regular reboots and even factory reset, but occasionally still happens.

Anyone else seen this?

[Re-Titled by Moderator]