The FET is supposed to be the SIR800 posted before, this is what I used in the drivers I hand made and have not heard of any issues with the 100+ that are floating around.
The production drivers though have used fake FET’s in at least a few of them, it was supposed to be corrected but no idea if it ever was.
The fake FET’s are most assuredly a problem and not up to the task of this light for extended use.
Without specialized equipment it can be very hard to test an FET properly. It is generally easier to just swap it out and see if that fixes the problem. This is the first thing I would try personally, for the $1-3 it would save a lot of time in the long run.
The other option is the small FET for the 1st channel could be an issue as well but far less likely since it sees a max ~0.5A.