I remember there was a similar issue in FS2Crew for the PMDG NGX happening right after asking the FO to run through the secure aircraft checklist and luckily Bryan was able to find the culprit and fix it.
Is there any chance you could do the same for GSX stopping this split second pause/freeze from happening?
Just because there's a pause, it doesn't mean the reason, let alone a possible "fix", would be the same. In this case, I think the pause you are referring to, is the time the sim takes to find the Simobjects GSX asked for.
At that time, GSX it's just asking for a title and, with all the different liveries and vehicles variations, the sim is searching through thousands of files so, considering what is doing, is fairly quick. It's likely the pause duration is related to the total number of Simobjects you have installed so, for example, if you have 10.000 AI models, it would add to the search time too.
Unfortunately, this is totally outside of our control.
It might be nice if we could tell the sim to only look into a specific folder, when creating a Simboject but, that's not how it works: you just supply the name of the object, and the sim will find it in every folder it knows were Simobjects can be located.