I’ve noticed this a few times on my rides. Basically what happens is Zwift effectively drops the ERG mode with the Kickr, thus not registering the hills or decent grades, but it still registers the power meter side of it. I’ve tried repairing the device, but ultimately it requires me to exit Zwift and then restart my ride all over again. Sometimes it happens during a ride other times if I walk away for maybe 30 seconds it’ll just drop and never return.
Same happened to me after approx. 20 minutes ride. When it happened, my ride stopped with a paused message even though I was continue pedaling. After a couple of seconds, the paused mode went away but the ERG mode was dropped. OSX 10.9.5, Garmin Ant+ USB, Kickr Firmware 1.2.2
The easiest way to fix this without interrupting your ride is to use something like the Wahoo Fitness app on an iPhone to switch it back to sim mode.
So I see where to do it but wouldn’t that override Zwift? I’ll give it a shot next time it happens but I remember having an issue before, when I started on Zwift, to where the Kickr took it’s resistance commands from the Fitness app and not Zwift itself and basically I had to manually input the slope, resistance, etc.
I also have a Kickr. This happens to me (and many others) when the ANT+ signal drops. It has happened very rarely since I put the ANT stick on a USB extension cable and moved it closer to the Kickr. This has been a common problem in the community.
I’ve been having this issue upon entering Zwift, when first starting a ride. I’ll have to exit the program and restart to fix the issue - as you noted, repairing the Kickr doesn’t do anything. I haven’t encountered ERG mode dropping during a ride though.