Im no expert but in Rouvy’s Just ride mode erg is disabled. Might be completely wrong but do you think its possible that erg mode on TR is clashing with Rouvy? I would try disabling erg in the TR app and see how you get on.
If its a bandwidth issue then you could try downloading the TR workout so it no longer reduces your internet speed.
Like I say Im no expert but might be worth trying if you havent already thought of it