Addon does not load I get lua errors (for example LSAC.logs error)

Try removing all addons from your server except the AntiCheat. If it works, then you know one of your addons is overwriting one of the basic gmod functionalities (which it really shouldn't). An example of this might leaks which contain viruses or backdoors inside or bad "exploit scanners" from steam workshop.

If the message contains the word "unsuccessful" or "HTTP Connection Error" somewhere, chances are it's just a connectivity issue related to your server itself not letting HTTP requests through and it will go away on its own