The issue is still not fixed, however there’s a workaround. Since 34.20 the changing booth finally allows one to set vehicle cosmetics, the player needs to re-set their vehicle cosmetics within the map using the changing booth in order for them to apply correctly. It seems that the main issue is only for loading the cosmetics presets set in the regular pre-game locker.
cc @Flak that’s my new finding on this issue. 