Some of the planes (e.g. CubCrafter NX) currently have problems with exterior lights (cockpit buttons are disabled), so they are indeed not working. For others, the new lighting model seems to have made them less visible. Hopefully that will be adjusted in time.
There is also a related problem where the interior lighting from the cockpit panels, when viewed externally, is flickering due to those textures apparently being refreshed/reloaded rather slowly (similar to when you switch between external and cockpit view).