unable to join my friend's world

i want to play with my friends on the minecraft windows 10 version, but whenever i try to connect to their worlds it always says "unable to connect to world". i didn't have this issue last week, it started a day or two ago. my friends play on minecraft pe and the console edition, but i was able to join their worlds before so i don't understand what's wrong. my wifi is stable and so is my friends'.