Unable to activate ritual alters

I ran into a map that had two ritual alters that don't have the popup that you click to activate the ritual fight. I killed the monsters around them, but I still can't use the ritual. The entire map was down to 4 monsters. My guildmates say there's an issue where monsters are stuck beneath the terrain, making it impossible to kill them, so that might be my issue.

Bug Report ID: #2086883550

Side note: I've heard of rare monsters being beneath, or looking like they're "swimming in" the terrain can make it impossible to complete a map.