If the parking brakes works before a restart, it means it is configured correctly in the airplane profile.
That is assuming you ARE using a custom airplane profile. Since none of the Prosim airplanes are internally supported by GSX, it means you must create an airplane profile, and the parking brakes test can be customized, in the case the airplane doesn't use a standard variable to test it.
So, the first question would be: are you using an airplane profile (you should) and if yes, how the parking brake test is set to ?