Bump, I am having the same problem on ASA.
PreventOfflinePvP=True
PreventOfflinePvPInterval=300.0
These are the settings I have enabled for me, but it straight just doesn't work.
It's under [ServerSettings] based on the wiki for https://ark.wiki.gg/wiki/Server_configuration#GameUserSettings.ini
I've also tried using them in the command line arguments, but that didn't work either.