I have noticed this in Durotar and Elwynn Forest in particular, but I know it's happened in other zones. With only Carbonite enabled my fps drops from 50-70 down to single digits. No errors reported as far as I can tell when I add BugSack to capture. I'll add any other zones I find as I do the world tour for Honor the Elders this time around.

If there are many icons on the map it might drop FPS.

Solution: disable nodes mining/herb etc if u are not collecting and/or zoom in map to narrow the count of icons refreshed on screen.

My workaround was to save a good specific map scale from outside the dungeon and whenever I'm inside the dungeons and it re-scales to the MAX with frames begin to drop, I'll just "restore map scale" and it goes back to normal. But it doesn't last long :/