It's a new error in 3.3b2 -- it worked fine in 3.3b1. And the maxiwatt is very compact and heats up fast, it's not like there was a plateau.
I just started a longer print, but after that finishes, I can try again and post the temp graph that shows the heatup is not plateau-ing. I also don't get the usual error message about the heating being too slow or anything, just straight heater fault.