Adding another source that could cause this issue:

In the module settings of the project -> module affected -> check if the folder of the classes that you want to import, are set as "source folder" multiple times.

If the folder is present multiple times IntelliJ will have internal conflict and will start to add the classes in the folder only by their fully qualified names.

Remove the voices of such folder until only one remains and then do a maven reload.

Now the classes should be imported correctly on top of the file.