How does the problem look like?
So when loading a map from saved files, the map difficulty should be greyed out because it was already selected at the start of the map.
In herowo, the map difficulty can be changed when loading a map, however, not sure that it also reflects
What exactly did you do to trigger it?
Loaded a map from the menu and changed the difficulty.
On which map it happened?
Island of fire, knee deep in the dead.
A screenshot or video would be fantastic.