I encountered the same problem as in this issue. The fix was to use an application manifest file and declare the application as being long path aware (see another forum post). The issue should be closed IMO as dirEntries should throw an exception when your program encounters a long path while not being declared as long path aware (it would then match the behavior of std::filesystem:::recursive_directory_iterator when using Visual C++ which throw a runtime_error when it encounters a long path unless your program is declared to be long path aware in its manifest).
I am not able to create an account on the DLang's Issue Tracking System so I cannot post this there.