Hi mate,
I think there's a few reasons why, one of them might be the contactors inside, if they are going HR that might be putting too much strain on the IGBT also the brake relay gets very burnt this may be contributing by not getting the correct voltage to the brake coils, I've studied a lot of these units & it all seems to be a common thing, that they might be running close to there limit most of the time, it's a good thing to keep an eye on such things as the load weighing device on the monos, as crash stopping can throw them out, just my thoughts!