What is elm-make: Map.!: given key is not an element in the map

Question

when compiling with elm 0.18 I'm getting elm-make: Map.!: given key is not an element in the map, but I can not seem to find any error in any List.map.

edit: I have a fix (posted below), but I would still like to know what this error means and where it comes from.

Answer 1

deleting .elm-stuff and reinstalling packages fixes the issue.