Hi, same thing happened tonight with me (client) and another player "unckelh420" (host). Both PC, random matchmaking. Bounty worked fine for first exolizer, but then refused to spawn a second (timer sat on 00:30 and never moved, while Thraxes came insanely fast, had 6 up at once at one point!).
Eventually somehow the host managed to get it to recognise the extraction, and we pulled out, Bounty failed.
I, however, managed to get all the pickup loot (we had a bit of Thrax spam, too, so not too shabby!) apart from the Plumes from the Angel and random spawn collection, but the host did not.
Not sure if he'll submit a ticket, he seemed to be resigned to it being a lost cause, but if he does, have the screenshots of the loot he should have gotten to at least get the same as me. And even if he doesn't, it'd be nice if he can proactively get what he missed out on if at all possible.