Abomination T17 boss fight duplicate bosses spawn, are unkillable

Reference number 206 999 127

First time I had maven in the fight, dunno if relevant. As I fought them, all of a sudden ghost of doedres (as if she was killed) started appearing, at highest I had like three of them. Eventually the final form (the one that spawns when all three initial ones are dead) spawned, but all the OG guys were still around. Some ghosts also appeared and disappeared occasionally. Whenever and OG guy was taken to roughly half health, they would full heal. Random ghosts maybe spawned then.

Anyways killed the final form eventually, and it dropped the loot like it should. Others did not die, tried killing them for a while but they kept healing. Random ghosts continued appearing.