You are going far too quickly, so I have a bit of an hard time following you.
When you go so fast, you are making everything more difficult for the editor, don't forget it's GSX is running completely external to the sim, and it's communicating with it through Simconnect, and the editor is constantly creating and destroying objects, and it's doing this while trying to maintain communication with the sim and await the replies.
Try to go slower.
Also, I noticed you always press the Disable barriers button. Does it work better if you don't, or you do it after the parking is customized ?