glitch/bug in kiln?

i got summoned for some coop in kiln, and the first and third time i got
summoned the msg victory achived appeared and i got the souls while we
were fighting the third black knight, the one on the bridge. how was
that possible? the host was standing right next to me both times it
happened. i msg them and asked, but they didnt know either. anyone else
experienced this, or heard about it?

Never in the Kiln, though, admittedly, I don't do much co-op/PvP there so I'm not in the best position to comment.

Discounting that, it sounds like a decently common glitch. I get some pretty weird ones in the forest from time to time.