My sister could join my server the one day, 2 days later not anymore. This continued for a few days now, I also can't join her world, nor can my brother join.

Like I said in the summary, my sister can no longer (since a few days) join my minecraft server. I have multiplayer on, we're on the same update, on the same wifi network etc. Let's say on tuesday she tried to join, and it worked perfectly. Thursday she tries again, but it says "unable to connect the world". So, we try to restart our devices, restart minecraft etc. but norhing works. Now, 3 days later? I'm starting to get a bit annoyed.. Because I just don't know what to do in order for it to work. So I thought, the only possiblility left is a bug in minecraft itself, so that's why i'm reporting this (possible) bug. Hopefully you can do something about it.