The issue could be from overheating, but it is unlikely.
If you were to take the back of the wheel off so you could look inside, then turned on the wheel, bound it to a PC and then turned the wheel. While looking inside the motor cans, you would see BOTH motors sparking. (on a wheel that either will fail or has failed) This is typically due to issues with the commutator or how the brushes are contacting it. It's very typical on cheap motors.
I'm not going to get into the how and why of it here, but this was not an issue on the single motor wheels. (or it was much more rare) The first place I'd look, if I were Fanatec and I am not, would be the way in which the motors are being driven. That's all I will say on the subject.
I have taken apart one of these wheels to diagnose the issue and observed all of the above first hand. I even placed each the motors on an oscilloscope to analyze their output as they were rotated at a constant speed.
Good luck and sorry about your troubles.