I also noticed that the ground handlers I type in the parking settings box are mostly ignored. Same for the catering handler. This second issue has been happening since the end of May update.
This is not an issue. It's how GSX was always supposed to work so, it's really a fix.
The parking codes in the parking spot should NOT directly decide the handler. They should only give a preference, but only if the matching code is for an operator that would otherwise always being chosen, being with an higher score than all the others so, parking code in the parking, were *supposed* to be used ONLY as a tie-breakers for all operators at the maximum score.
However, it didn't work exactly as documented, so using those codes, you could affect the choice of the handler directly, and being able to select handlers which wouldn't be chosen otherwise.
The update you are referring to (in fact, it's not the end of May update, which didn't change anything about codes), it was the one at the end of April instead.
That update, which allowed to choose MULTIPLE EXPLICIT operators (it wasn't possible before), made using parking codes obsolete, because now you can choose any (multiple) operators, bypassing completely the built-in rules.
So the parking codes are finally back to work as originally designed, just as scoring boosters, because the new system is far easier to understand and it gives you more flexibility.