There’s a current soft-lock bug in the game when attempting to complete the Stronghold. You can avoid this by doing the following
Enter the Dungeon
Hop on your horse and run around all the areas to spawn trigger all the enemies and Lieutenants
Go back to the middle and kill the bottom left Lieutenant that drops the key.
Kill all other remaining enemies that AREN’T Lieutenants and open the door on the far-right
Kill the Lieutenant and his enemies
Kill all remaining enemies until the bar is full and kill Lieutenant at the top-left
See https://i.imgur.com/H61n9Nl.png for order
To Blizzard: In short, the bar has to be full before you kill all the Lieutenants. If you kill all the Lieutenants before the bar is full, the game soft-locks
Bug fixes aren’t a revenue stream so Blizzard don’t give a f***, and quest script writing is hard it seems.
In my case the 4th boss, the one I think the OP refers to as the one “at the top-left” isn’t spawning I only see 3 boss icons and 3 red Stronghold ones, is this the ‘soft lock’ Havi is referring to?
Thanks to Havi for posting this, it just broke on me again so I’ll try his tip next time it resets.
[edit]
So taking Havi’s tip of riding around to spawn mobs I ended up aggroing and killing the key dropper BUT I noticed a second boss icon nearby and that proved to be the 4th boss that had never spawned before.
In the end I killed the key dropper, this ‘new’ one and the boss in the cave before filling the bar but was still able to kill the 4th boss on the upper level that’s stood by the tower and then the main boss spawned.
So thanks Havi, it’s clearly a spawn problem that would be easy to fix if Blizzard cared about it.
