Restarted server and changed settings, and now I can't find the server on the Ark session list.

When making settings changes, take server offline for at least 5m. Make settings change, save, then restart.

If you are stuck now, remove the settings you made and restart again.

If this is a new server, doing a reinstall probably is the best option. That way you will know you have a stable, running server.

Then make your changes. If server gets stuck in restart on an ini or setting change reverse it back. More than likely its the code you are trying to use.