Yeah, that's happened to me too. I spent an age trying to beat one of those while at a very low level because I suspected they drop the Hox Daylight Spur needed for Colony 6. It was always a game of trying to single out one of them and keep it as far away from the others as possible while not going out of range, but even alone it was impossible to even hit. In the end I managed to beat one by spamming debuffs as Riki, and I didn't get the drop, neither did I get any of the "fight a higher level monster" achievements. Blarg.
I still don't know if they even carry that item.
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