11.20 update sort of fixed everything!?

What trainer and HRM are you using?  I use a Cyclops Hammer via ANT+ reading power and speed.  I'm using an ANT+ GSC10 for cadence as cadence from a trainer is not reliable since it's derived from power pulses rather that actual crank rpm.   And either a Garmin HR strap or Scosche optical HRM, both ANT+.  This has been working reliably for me. 

H2 and Garmin Ant+, it will happen on the road also. Need to do another test and see what happens. In Zwift it never dropped, but on the Edge 820 it did.

Not that I am happy at all with garmin software, but so far i had no issues with HRM, cadence and power data on IRL rides. BUT It happens quite often now that I see HRM drops frequently and power drops also in my pain cave. Actually I won't blame garmin because on my computer running Zwift (and therefore independent ANT+ inputs) I see also frequent and even more frequent drops. So I guess some electromagnetic interferences (my HT is in between two big water heater tanks) can affect ANT recording, but not this not related in my hands to garmin or Zwift i guess

And I have to had that these drops do not occur if I do HT in an other room

Yeah.  I've seen issues indoors running Zwift on a computer/tablet.  I use a USB extension cord to position the ANT+ dongle close to the bike and trainer.   Using a tablet on a stand in front of me, I use a 2' USB extension cord to move the dongle away from the tablet.  This has been reliable. Though this isn't a solution for the 820 dropping sensors it does suggest that interference might be a possibility when running indoors. 

IRL Edge 820 test. I soaked the Garmin HRM strap and it worked great in my 10 mile ride. In the past, I only had to slightly wet it and it worked great. I will soak the strap from now on and hopefully there will be no issues.

 Wasn’t having any problems before the update. I had fixed my earlier Di2 issue with the last update and everything was working great. I am happy to report for this update, it did not appear to break something else. For one 50 mile ride, everything worked as before the update. 

UPDATE: Started Garmin Edge 820 with Garmin Connect and Garmin HRM, this setup kept disconnecting and giving heart rate in the low 90's bpm when it should have been in the 150's to 160's bpm. Disconnecting Garmin Connect fixed the issue. Last 10 minutes of ride I connected Garmin Connect and had no issues. 

I have big problems with Edge 820 dropping power sensor (Stages) since version 10.00 (it constantly drops every minute then reconnects it back and this repeats during entire session).

V 11.xx brings no improvement, hard reset didnt help either.

Garmin service refuse to help me (because "they only support Garmin PM", they said).

Last year with older softwer had almost zero issues, my smartphone with dedicated bike programs works without problem (ANT+/Bluetooth)

I hope next SW will be better.

My issue seems to be resolved after getting a new HRM, it seems to transmit with no drops or erroneous numbers at this time. Hopefully it stays that way.