i had that quite a few times, comes from injecting too much volume too often in my opinion.
i can inject 2.5mls into delts no problem, when i rotate left / right delt, left / right glute. after 2 or 3 rotations i HAVE to pin a different spot than delts, otherwise these lumps will form.
for me when that happened it usually hurt like a week and then stops hurting but theres still this "lump" inside that doesnt go away on its own.
the swelling can actually give a capped look to the delt lol, but sometimes it seems to "wander" down and sits between the point where delt, bi and tri meet and it looks shit.
i actually had to drain my shoulder 3 or 4 times.
one time i thought it was gonna go away on its own so i waited like 3 weeks. in the end i drained about 10mls of oil/pus. the inject was only 2.5mls, so go figure, lol.
if you drain it shortly after the lump forms its probably only 3-4mls.
but i had to make sure i drained EVERYTHING out. like when i left a tiny bit of oil inside of there it still was not getting absorbed.
when i read that it sounds pretty fucked up actually. but was no big deal at all