Unable to connect world

Hello! I'd like to complain about an issue that has been ongoing for about a month now

so me and my friends have been playing survival for about a month now, and within that time span, when i try to join the world sometimes it works and I am able to play with my friends, but other times it doesn't work, No matter how many times i tried to join. it always says "unable to connect to world." The time span between being able to join the world and being unable to join is random, sometimes it takes a day, sometimes it takes a few hours. I've tried resetting the WiFi router, I've tried restarting my phone, I've tried logging in and logging out, basically I've tried everything. so did one of my friends who is the owner of the survival world we play in. I'm wondering if this is some sort of server issues or a bug? I'd appreciate it if you could sort out this problem. Thanks!