So I also had the Wahoo Elemnt Bolt connected via ANT+ once I saw the bug again. The Wahoo was unable to control the trainer until I stopped Zwift, which tells me that Zwift was in fact controlling the trainer, or well, blocking anything else from doing it.
The ride that triggered it was odd. It started out fine, then it cut out multiple times, with resistance going high, then it worked again for a minute or a half, and this three times before I gave up. I changed the trainer difficulty level directly before this started happening, but I don’t know if that causes the issue or not. Wanted to set it to 100%. For trying that out, you know. After the issue happened, the slider to set difficulty was gone.
I then went to control it via the Elite app which worked fine(*), both ERG mode and video mode seemed to work. I also tested with the Elemnt, which was able to adjust resistance as well.
Deleting app data and restarting did not help, neither did removing the trainer’s power for 10s. My assumption given that Elite’s app and Elemnt work is that Zwift is not communicating correctly with the trainer.
(*) OK well I was going 140W and it was telling me I was travelling at 10 kph, when it previously said 40 kph. But it was able to change resistance.
Edit: FWIW, after doing 140W ERG mode in Elite’s app for a while, resistance in Zwift was low rather than high, but did not change, so I was going up hills like they were flats…
Edit 2: I have submitted a support request with log files for the issue now, it’s getting even weirder here now, as it is fine for some tens of seconds or so, and then resistance goes up again, if I pedal through, it becomes fine again for the same time, then goes back up again. Oh dear.