This bounty bug has been around since the dawn of Diablo III. First reported bug on this was back in October of 2014. To be blunt, the bug is that the bounty is incompletable. You can enter the hideout and annihilate all content mobs, etc. You can leave the hideout and return. Nothing you do in that bounty will complete it.
Now to discuss the emotional drain it is to be running with your clan mates on a group bounty. Either you join a group bounty or open a bounty run to the public. Your merrily racing to complete all 5 act bounties as quick as you can. Then suddenly, your wondering why your Act V bounties haven’t been completed and then the dreaded reveal appears before your eyes as you notice player x stuck in Act V. You ask in party chat, “What the hec is going on?” He then responds, "I can’t complete this “Hideout of the Lost Legion.”
It’s at this point that your completion of Act V comes to a very tragic end. If you have any sense, you just tell the group that they must leave game and complete Act V on their own or if you’re a sadist, you can tell them that you’d be happy to invite them (one at a time) to just go and re-run Act V bounties.
Personally, since we’re now getting double bounty’s in Season 26 to celebrate 10 years of Diablo III, this leaves you still evermore excited to go run that Act V bounty on your own. This is just a reminder that Diablo III is an awesome game and whatever comes next will override the temporary pain and anguish of this minor set back.
Thanks for listening. Again. 