One thought is that your av install is rebooting your computer before the batch file gets to the sc command and the net start command.
I know this process works because that is how we use it today in our environment.
To track this we output each of the setupcomplete.cmd commands to a text file in c:\windows\temp using
">> c:\windows\temp\setupcomplete.log" appended to each command line. If the output cut off before finishing, we knew we had something interfering with the process. It’s not a perfect answer, but it helped get things organized.