Fable/story quest bug

There is a bug on one of the fable maps, I think the quest is "The Dudes Rift" (The one with 4 bosses)
What happens is the last boss spawns first and if you fight him and the second last boss at the same time, when they are both dead and the pop up is exited you won't be able to move/open the chest.
Pretty sure it has happened to me on the story quest of the same type too.

Known issue, plenty of other posts on it, but we've never been able to reproduce the problem here. The bosses shouldn't activate at the same time.