SW 24.12 - no sleep tracking & sleep HR broken

I have auto updates turned off but had to connect my FR955 to the computer to download a workout.  Must have rcvd the update then.  Since then, no sleep tracking.  Daytime HR seems fine, but overnight HR is either absent or spotty or constant for long stretches.  Anyone else?  I've looked through the settings - seems all good - and soft reset twice.  Still no help.  Any ideas what to try next (short of the nuclear, factory reset option)?