I am running 8.20 but have no idea what's in the changelog. My floors stopped working properly it seems, back in April.
Symptoms.
Floors don't count anymore except when on a GPS activity and then it's hugely out. I can climb over 500 floors on a flattish walk. 
When I check the barometer in the test setting, it says it's invalid.
I have gently cleaned the holes with a soft brush, but makes no difference.
All had been working so well but now having to recalibrate elevation with Strava for accuracy as can't rely on the watch to do it.
The watch is about 4 years old.