[BUG or HW?] Sudden rise in HRV?

Look closely at the brightness of the flickering lights of the optics.
If they shine a little weaker, less brightly than usual, this may have contributed to this upward jump in BCP measurement.
The "cure" for optics operation in such a case is to reset (off - on) the watch. Observe the result the next night.
There was also once an increase, due to optics light failure, but a little less.
Good luck, you will never get bored with your Garmin watch.

Wow, that may actually be the cause, they shined very weak now! I've now restarted the watch by holding light button until it shut, and now it's back to full brightness again. Lets see how HRV looks tomorrow...

Yes, I've seen the same behaviour (and reported it here) a couple of times, a force reset has so far solved the problem.

But Igor Petrov's comment about the HR sensor lights being dim is interesting! I haven't checked them when the problem appears, but I'll do the next time.

Garmin-Sierra, you mentioned in some other threads that Garmin team has come to the solution that this is caused by bad placement of the watch on the wrist. This (and my own experiences) don't support that, since force resetting the watch seems to cure the problem even though the watch is worn exactly the same way after that.

The last thing I did before this "kicked in" was a Walk with a chest strap and the watch worn on top of the sleeve. Could that maybe be related...?

OK, so LEDs shining weak seems to have been the issue then, since HRV now is back into the normal span after the forced restart.

But it makes one wonder, is this due to software or some fading hardware? I've never seen it before and have had the watch for a year now, but I guess I'll have to pay attention to the LEDs from now on then...

Since this is (mostly) fixed by rebooting, it's almost surely a software/firmware issue. And I've occasionally stumbled onto this problem since last October, and it has not become more frequent, so I'm reluctant to believe the hardware is failing.

Ok that's both good and bad I guess... The big question is what triggers it now then?

All, 

Thank you for your comments. oBuTTuSo, I'm not sure why the green lights would have dimmed...if this happens again, would you mind taking a before and after picture of the lights after powering it back on?