I did a flight without GSX...door 1L didn't open on arrival.
It might still be related to PMDG own automation, which is detecting GSX when it's running, but not doing anything when GSX is not running.
There is a specific issue with the 777-F though, and it's a problem with the Main Cargo door.
In the passengers versions, PMDG has added a variable (following our request) we can check from GSX to know if the PMDG ground vehicles are present, so we can send them away, this works fine with the passengers version, but the Freighter version doesn't have the same variable for the main Cargo door, so if you start a flight with PMDG vehicles attached, GSX cannot reliably know they are, resulting in a possible opening/closing of the Main cargo door. I need to check with PMDG again and ask if they could add the same variable they added for the FWD/AFT loaders to the Main Cargo door Loader but, other than that, there shouldn't be any other issues.