This indicates that there is an Oracle dictionary problem when resolving an identifier.
To obtain some more diagnostic information, can you modify the PL/SQL Developer shortcut and add the DebugSQL parameter? For example:
"C:\Program Files\PLSQL Developer 12\plsqldev.exe" DebugSQL
Reproduce the problem and send me the debug.txt file that is generated in the %APPDATA%\PLSQL Developer 12 directory (e.g. C:\Users\\AppData\Roaming\PLSQL Developer 12).
To suppress the issue you can go to Preferences > User Interface / Code Assistant and disable the "Automatically activated" option.