To obtain some more diagnostic information, can you modify the shortcut and add the DebugSQL parameter? For example:

"C:\Program Files\PLSQL Developer\plsqldev.exe" DebugSQL

Reproduce the problem and send me the debug.txt file that is generated in the PL/SQL Developer directory or in the %APPDATA%\PLSQL Developer directory (e.g. C:\Users\<User>\AppData\Roaming\PLSQL Developer).