Normally, for the last couple months, I have been using my MacBook w/out issue. I just tested my iPhone in workout/ERG mode for about 10min. Everything worked as it should.
I am not able to completely test w/my AppleTV. Bike is in a different part of the house. However, I did pair my HR monitor for comparison against my Garmin. I watched that for about 5min. All good.
Noticed you said your HR was 170bpm via Garmin and 141bpm in Zwift. If so, I would not be so quick to blame Zwift. You should double check your device pairings. I used my AppleTV for over a year w/a Tacx Neo. HR has never been an issue. I have had a loss of resistance, but only a couple of times. H3ll, it could have been signal interference for all I know. If I get a chance later, I will move the bike and test ride w/my AppleTV.
Again, double check your device pairings.