People can't join my LAN game.

My friends can't join my LAN game on the same wifi network. I can join theirs but they can't join mine. They have joined in the past, but no longer can. I know know if it matters but this world they can't join was copied on to a realm (not copied from one) and is 41.7 MB large. PLEASE FIX THIS BUG UP I PUT A LOT OF WORK INTO THAT WORLD. Also my multiplayer was on.