Delirium Wave: 16/15

Possible visual bug, after completing wave 15/15 in a tier 2 Delirium encounter at Clearfell Lumbermill.
Went to hideout then back inside the encounter and Strangely Familiar Entity offered to start wave 16/15.

Unable to actually start the encounter so it seems to be a visual bug?

Ref Number: 3917163573