Same issue here, I’m in touch with Support@ and looking into it.
In my case, restarting the entire phone is not required, turning bluetooth off and on again does the trick (and usually, fixes it “for good” for the training session). Funny enough: ANT+ (my cadence sensor) keeps going with no troubles.
I am currently excluding an issue with the trainer/power-meter because (1) Zwift (running read-only on a different device) keeps reading numbers fine from it while TR drops out and (2) the HR strap drops out too, at the same time and in the same manner.
I just removed the app from the list of Samsung’s “Battery Optimisation” ones, I’ll see if it makes any difference. If not, next I’m going to try with a different phone (I have an old iPhone sitting around) to validate my hypothesis that it’s an issue with the phone/TR interface (you aren’t using a Samsung by any chance, are you?)