My response is sort of all over the map here, maybe the converter ballooned, maybe it didn't have enough space to begin with, but I would likely be asking about pressures, stall speed options, and limiting feed to the converter too if they think its appropriate, lots of tricks guys do to make them live and be consistent
Before that I would look very close at pilot hole alignment, it seemed to take a beating too, to include size of the hole, flywheel and converter "marriage", but I do think something is certainly there
Option 1 - The flexplate/balloon plate/bolt head/relationship was bad and you tightened the converter against the crank bolts and pilot hole. This would cause the marks, but only cause thrust bearing failure if there wasn't enough room on the backside of the converter, jamming the crank forward. I'd ask what you see on the pump side of the converter, maybe there are some tracks
Option 2 - It all fit great and the converter grew. Possible, and happens, but IMHO you likely aren't making the power for that unless you have a tranny problem or the wrong converter, because it is an antiballoon converter. Diameter matters, and maybe with the transbrake, the converter just doesn't have the capacity for the launch RPM and you were driving it to the limit for that size converter and it grew. It also could be that you weren't binding, but didn't have enough room for it as it was at pressure. There is movement there.
The hard part is, regardless of the scenario above, indications will be the same, converter pushes on front pump and crank, thrust goes out, so you may not find THE answer, but you may find where your setup was marginal and give it wiggle room
I am not an AT guy, but I understand that dump valves and limiting converter feed is common, I also think that if you are at the limit of the converter, adding a couple hundred RPM or more of stall might help make things live longer.
Keep in mind, getting all the way to true stall speed (and the internal pressures associated with that) with a transbrake will be higher and greater than footbraking, so if the converter wasn't designed for that, it could be working pretty hard driving option 2 above