Don't know what's up with that, but I still think it is about the failed runs. (Icon + its name makes also more sense for this case)
I also haven't seen any popups for a long time (Steam at this point had already ~300 hours counted and still no popup). However, roughly 25 hours pure idling while not being at the pc and retiring the dungeon when I came back I got the 50% completion popup. Coincidence? I don't think so.
Maybe you want to try the same, if you got the 75% mark already it shouldn't take that long to reach the 100% then.