FlatFace1015

This is still a problem if anyone knows how to fix

So for some reason whenever I join my server it will kick me for no reason and shut down the server, saying that the server is sending me to a fallback server. But when friends join while I’m not online, the server tends to work and not shut down. Ive tried repairing files, turning off command blocks, and continually restarting the server. It still doesn't work, also I do not want to reset the server because I’ve put loads of hours onto the world. Anybody know how to fix this?