If you run into issues while joining the server that displays an error for "Host has left server" there is currently a temporary fix for this.
Unfortunately this will have to be done when ever the server is restarted.
1. Log into your Clanforge service.
2. Select Space Engineer
3. Files > SANDBOX_0_0_0_.sbPB
4. Tick this file and select "Delete File"
5. Restart server.
By this point you should be able to connect to the server, however if you run into any further issues please contact our support team to investigate into.