I board just 1 seated passenger and as soon as the beacon light is switched on, the sim experiences heavy stuttering.
As far as I know, the ini A350 doesn't start Pushback when you turn on the beacon light, doesn't it ? If that's still the case ( I haven't tested it recent updates, so I'm not sure ), than it's NOT related to GSX creating objects for Departure ( just 3 objects: the main pushback operator and optionally 2 wingwalkers, everything else is already there)
I am a big fan of GSX and have owned it since day 1 but I'm convinced that this is a GSX issue.
If it's confirmed the iniBuilds A350 doesn't start GSX departure when turning on the Beacon light, it completely clears up beyond any doubt this issue is NOT caused GSX, and it's JUST a result of the new dynamic light projecting over a much more complex geometry ( because there are passengers in *addition* to the airplane cabin ), which means there's just nothing we can do about it. You can, of course, not use Seated Passengers, at least not with the airplanes with the most complex internal cabins.
I think I repeated multiple times that, after everybody is seated, GSX
lost any control over passengers: they are just part of the airplane so, if we can discount the hypothesis the stuttering was caused by GSX creating the Pushback crew (which happens on the Fenix when you turn off the beacon light), the only explanation left is just the newly added dynamic light affecting the sim because it's projecting over a much more complex geometry.