This started to happen with the latest update. It worked before
You said you are using P3D 5 so, it's not possible it started to happen with the latest update and worked before since, before this update, ULD never had ANY livery, they were blank. Maybe you wanted to say they turned from no logo to random logo ? That's more likely, but it doesn't happen if you configure the codes correctly, as explained in other posts of this thread.
and my airplane (FSLabs A320/321) is correctly configured: atc_parking_codes=DLH
No, it's not. See my previous posts, the atc_parking_codes should match the codes used by GSX for a specific operator, not the parking codes that operator might be matched on parking spots. Those codes are the names of the sections in the rules_handling.cfg file in the Addon Manager\texture folder so, for example, the section for Lufthansa is:
[LH]
couatl.atc_parking_codes = DLH,DLHX,LHT,CLH,GEC
couatl.icaoprefixes = ED ET EDDK EDDS EDDB EDDN EDDH EDDM EDDC
couatl.basecolor = yellowSo your line in the aircraft.cfg should be:
atc_parking_codes=LHLH matches the name of the [LH] section. Now, even if I'm not sure the simulator itself really uses your own airplane parking codes, IF you want to better conform to its standard, you can set it like this as well:
atc_parking_codes=LH,DLHThe first LH will make GSX choose the LH containers, while the second one might be used by the sim to assign you to a specific gate ( I'm not sure it does ).