i had this as well (atv w latest ios, h3) but i might have fixed the issues as i was able to complete the 8 workouts and 4 group rides of the zwift academy without any issues. in the beginning before my changes to the procedure and system, resistance was lagging and sometimes a dropout.
-applied stabilant 22 to the power plug tip, this increases conductivity of the power supply
-moved the atv to the left side of the bike/h3 at 40cm distance. this improved signal significantly
-moved most of the wifi devices to 5ghz, inc the one with companion
-allow only wifi ch6 of the 2.4ghz band. this gives enough (discovery) channels to ble and ant+ (i use ant+ to record ride on garmin 530 at the same time).
and now important, before i close the atv, i swipe away all running apps. and before i start a new ride , always reboot the atv.
if i don’t reboot, i might get lag in the ride again resulting in 400 watt during downhill…
also, i do all my workouts on tempus fugit, most of the issues i had was with hilly rides. it also looks strange doing a 100w segment on a 6+% so i keep it a flat route for these workouts.
the only thing i still have is that cadence is sometimes erratic. fluctuates a lot between 75-100 during fast switching segments in a workout. (with erg on) difficult to get the stars then.
Will soon openup the h3 for maintenance, and probably put extra fan on it for additional cooling of the electronics