You are making all your comments based on a single thing that, if you searched the forum, would have known it a problematic scenery, that is Gaya LOWW.
You haven't even said if it was the Marketplace version (which GSX can't use) or not but, again, if you searched the forum, you would have know this scenery have some issues even in its regular unencrypted version.
Looking at logs from several users with the same problem it seems that scenery is missing the "Delete Airport" record, which is an indication for GSX the scenery is not a complete airport, just an enhancement, so GSX will always use the default airport in those cases, and of course it has been like this SINCE 2012 with GSX came out: it will only work if an airport flags itself as being complete and not depending on default data. This hasn't changed since FSX.
I don't know if Gaya LOWW is really supposed to be only an enhancement of the default airport, or the missing Delete Airport record is just a mistake, GSX cannot obviously know about that, it must trust that flag to know if it need to use the default airport or not, and most of 3rd party airports DO have a Delete Airport record, unless they are really supposed to only enhance the default.
Of course all of these issues with problems with .BGLs that might contain errors will be gone once we'll update GSX with the new Navdata API that just became available with SU10, which will also allow to use Marketplace airports but, in general, it would have been best if you tried GSX on other airports, instead of assuming GSX "has a problem", only after trying a single airport.