Ambush Scarab of Containment not spawning Ultimatum Encounters

Ultimatum encounters do not spawn on maps with Ambush Scarab of Containment.

I've replicated this bug using 100% Ultim Encounter on the Atlas Tree, the Ultimatum Scarab, and the Ultimatum Map Device option on separate instances with Containment.

Encounters that don't seem affected by the bug as they spawn with seeming their 8% chance:
Legion, Blight, Ritual, Breach, Expedition, Harvest, Delirium, Abyss, Essence

As many other posts have said, this also interferes with Eldritch Alters.
On average I might get 1 alter, if I come across a shrine or Harbringer, but no more after that.

Eldritch influence is not affected, as the counter towards the Invitation goes up and the Invitation drops as expected.

Bump