There seems to be something wrong with the server. After 2 users got stuck in limbo after entering the ender dragon portal, the server crashed overnight.
I restarted it this morning but it seems to have been a short-lived fix since the server went down again.
The biggest issue is that I am not at home and can only restart the server via cellphone but not really search and fix the issue.
Please report here in the comments if the server is down for now.
Further, if the server crashes right after you login, please report it and do not login for today anymore since you might be the cause for it.