What trainer is it?
Wattage floor usually is the lowest resistance a trainer can deliver. When the power target rises above the wattage floor, the trainer should work like normal.
It could be that the trainer was not being controlled by the TR app. I’ve had this in the past where the TR app was connected to my trainer (Elite Direto), but it was not controlling power - and I could only get the power higher by pedaling faster (and only up to about 100W at over 100 rpm).
The solution at the time was to shut down the app, power-cycle the trainer (power off, then back on) and start over. Might make sense to give this approach a go, and see if the problem repeats.
Also, for lower power riders, choose an easy gear - little ring, higher up the cassette. This lowers the wattage floor.
And this