do you see any visible damage or sharp edges and such in the inner barrel assembly?
also are the gels fresh?
coz even at stock setup i was getting a lot of AT milk shotgunning out of ebay alloy barrel,
which turn out was due to the gels being old,
after i made a fresh batch, that issue was eliminated until gels been left for a while.
also, no sure if this helps, but,
Galápagos J recently uploaded a vid on gel hardness,
which at the end he suggests to use certain gels with certain spring rating,
in which, if you exceed too much in terms of FPS, it will cause deform and even breaking.
from my experience with some of the gels he tested,
AT milkies would probably be around 1 stars rating on his chard,
which was suggested no to be coupled with spring more than M80 rating, which is about 260 fps,
so it might be possible that your FPS is simply over the threshold that said gels could handle?
if you have a weaker spring, maybe swap that in and see what happens?