it would appear by the example of the faults you are giving, that the respawn/spawn of your vehicles is done on the client machine
You need to "Server side Script" any vehicle respawn
to do this create a gamelogic named "server"
and then for the vehicle creation line in your script, simply precede it with the following line
?(local server):
or if the script is to be only run on the server then have the following line at the start of the script
?!(local Server): exit