BungeeCord kicks players to fallback server

Hello,

I have a problem, whenever players connect to one of my servers through bungeecord, they are all kicked after like 30 minutes. Then, when they try to reconnect, it kicks them immidietaly with message:

The server you were previously on went down, you have been connected to the lobby.

But, the server is still up, it just kicks the players from it

Any help would be great