I've noticed recently that a notification of a Rare spawn in an adventure area is sometimes not followed by an actual spawn of the Rare at the location marked on the map.

I got this with the Thum Grim event in Gianthold yesterday and a couple of times with Rare spawns in The High Road today. Get notification, dot is on the map and then when I arrive at the dot nothing is there. I swept the area around the Thum dot thoroughly because I'm looking for my 8th dragon kill in Epic Gianthold. No Thum.

Thumthing is not right...