Looking for reasons why 2nd and 3rd gear sets broke on a MK3 trans

Looking for reasons why 2nd and 3rd gear sets broke on a MK3 trans. The shafts look good, it has the roller bearing conversion. Starting the bike without any known history , and there were some bad, bangs/knocks.

3rd layshaft gear had damage also

No history will make it difficult to do anything but guess. It looks to me that something large broke off and got jammed between those 2 gears and broke the 4 teeth off. How you work out from the debris in the sump which is the guilty party and what are the ones that suffered is impossible. The whole gear set must be suspect as you don't know which are OEM and which if any are later dubious replacements,