I just had the same issue also with a TMap when I accidentally removed the struct used as the value…
Couldn’t find any reference to the TMap variable anymore after removing them all from the blueprint, but still had 2 errors when compiling about “Invalid type map of … to Structures”.
What I did was create a TMap variable in my parent C++ class with the exact name of the variable giving the errors (type doesn’t seem to matter). Then I was able to compile my blueprint again without errors.