Sometimes I get "Creatures in combat" false notification. When I click notification icon, it shows skarg in lair.
Hmmmm this case is meant to be suppressed I gave it a quick try with some Skargs in an Arena just now but couldn't replicate. We'll give it a more robust go in the new year.
Unfortunately I've not been able to cause this in any of my generic test environments. I don't suppose you have a screenshot of your Dungeon in this level or a save file that we could use to try a replication?
It's a rare bug. You won't get it more than a couple of time per mission.