Hello I have this problem when I use gsx and pmdg and I have a flight plan in simbrief. Thank you very much for the help.
This has been discussed so many times on the forum, that it's basically impossible to not find it if you searched it. It's not obviously a GSX problem, it WAS a problem with the PMDG 737-800, which had the icao type wrong in its aircraft.cfg to be B737 instead of B738.
PMDG has fixed it in a later update so, just be sure you installed the latest update for the PMDG.
