I had been using my CompuTrainer with Zwift for quite some time, without issue. It suddenly started raising Lost Signal errors on my paired devices. As soon as I started a race, my racer did not move. Did a lot of digging, re-pairing the device, re-connect the device, re-install zwift, nothing worked. Checked the forums and saw a large number of posts where people reported the issue and never had any resolution.
I came across this post from Asmund_Sandvand , burried in a very long forum post, which mentioned a preference file that might contain device IDs discrepancy (/t/no-signal-in-the-pairing-screen/71796/29). I checked the file under Documents\Zwift\prefs.xml and noticed that the LASTCONTROLLABLETRAINER ID was different than the other values. I tried to just change that ID to the same as the other values, and tried again. It worked !!!
Not sure why it changed, I was using only a single device, but this fixed the issue for me. I thought there was so many posts reporting this issue, I thought to share it.
So in the file, I just changed 536870915 to 536870916 for LASTCONTROLLABLETRAINER, and I was able to ride again .