Wattage problems

So I have had this issue a few times now, and don’t know if there is a fix, or if something is wrong with my trainer. I will be riding in Zwift, and keeping my wattage steady, and then the trainer without any notice will start getting harder and harder to hold the wattage, to the point that the only way to keep pedaling, even in the lowest gears, is to stand up, and even then, laying down as much power as I can muster, the wattage will read around 100. A few times it has gotten so bad, that the wheel will spin on the trainer but the trainer freezes. Anyone else had this happen?

What is your setup?