A lot of people have been running into a bug during the event bossfight against Captain Haunt in the Heck Hole. The bug causes Haunts immunity phase to become permanent, making you unable to finish the bossfight.
However, the bug can be easily avoided. All you need to do is to wait until Haunts pylons have begun recharging Haunts shields before you destroy them. The problem seems to be that one of the pylons takes longer to spawn in than the other two and if the other two are destroyed too quickly, the last one doesn’t actually spawn at all, making it impossible to end Haunts immunity. So don’t be overzealous and just wait for a few seconds when he enters immunity to keep an eye on his healthbar. Once the shields start recharging, all pylons are spawned in and are save to destroy.
If the bug still happens to you, there’s two ways of dealing with it.
- Dying to restart the fight
- Savequitting and loading back in (in which case you spawn back in before the fight). Arguably the better option if you have a reasonably fast PC.