HRV- average overnight data is completely wrong.

Seems more likely that the problem is in the graphs drawing. 

Try looking at the smartphone app as it has better resolution and detais.

Same problem with garmin connect app on smartphone. It's not a matter of resolution and detail. More than 50% of overnight measurements have the same error for average HRV.

Did you maybe change the sleep time afterwards? Since this seems to not trigger a re-calculation of HRV

No, I didn't change anything. 

Maybe it's the way Garmin calculates the average, like giving more weight to a given part of the sleeping time? 

More info would be nice. Garmin-Kevin 

Or maybe you really got bugged and will need a full reset.

All ok here, also in GC

Have you looked at measurements from other nights? My Forerunner 955 also shows good sometimes, but still a large part of the measurements are wrong.

yes the same thing happens to me. 

I have the same issue. It's even worse than the graphic I made. I transposed the numbers. It's actually 31/30, not 30/31. My watch has gone back to normal it seems.

https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/instinct-2-series/329235/hrv-status-calculating-error

It's affected some Fenix 7 users as well:

forums.garmin.com/.../1586889