https://steamcommunity.com/sharedfiles/filedetails/?id=2544434818

I wasn't sure if the troll was really red, so took a screenshot

https://steamcommunity.com/sharedfiles/filedetails/?id=2544438475

Travelling past the spot a few game days later, the blue Troll popped into view right in front of me.

I know it's not much of an "event" but does seem to indicate that there is some mob & base entry or exit occurring.