I can only confirm the problem is fixed in 2.9.0, and it could only happen with the PMDG 737, because it was caused by the fact that GSX, at the end of the Deboarding, set the airplane empty but, before the fix, instead of setting it at the very end of Deboarding (after the last Bus), it was emptying the payload after the first trip.
No other airplane runs this code, which is part of the custom PMDG integration.
Fact you saw it with the FBW A320, seems to indicate that, for some reason, the payload went low after the first trip, but I assure you it wasn't GSX so, maybe it's something in the FBW GSX integration that is doing something like what GSX used to do with the PMDG before the fix: emptying the airplane after the first deboarding cycle completes, without taking into account there might be other trips.