[1.2.3] Missing guardian in Ruined Dungeon

[Cadex]

I searched for this issue and saw it had been discussed in other forums, but not here, so I figured I'd report it just in case.

One of the six guardians in the Ruined Dungeon never spawned (or disappeared) no matter what I tried, so I was unable to activate one of the six pedestals. The NW room where it should have been was empty except for a couple normal creatures. I even tried digging most of the walls and no luck.

I then temporarily installed Marson's "Bosses Gone AWOL" addon as a workaround, and it did apparently fix the problem and made the guardian appear (it was a rare void horror).