[Edit] I posted this thread after having the impression, that an enemy troop had respawned with unusually low values. I have since then encountered some respawns and copies, in the same situation as well as in other types of encounter (for example delve Mirrored Halls, there even on both sides of the field) where this was not the case.
This thread can be ignored.
Like Fourdottwoone predicted here,
I suspect this may have some interesting side effects for summoned/tranformed troops, like bringing them in at level 1 in case they’ve gone missing.
This just happened to me during a pet hunt containing Infernal King. When he resurrected, he returned at level 1. I did not notice whether any traits were activated, and was not able to witness it once again during the 8 fight stretch. With practice fights being the one type of fight, where the issue can not be reproduced, it is a little difficult to check right away.
As has been noted, this is another side effect of the workaround to shiny mirroring.
Please consider some kind of different approach to the problem.