Cannot play with friends without WiFi

It's called Hotspot and wifi connection. I think they removed this feature a long time ago and the only way you can play with your friends is online or when your friends are connected to the same wifi and has internet. Hope this helps!

Do you have mobile data turned on? If not, why do you consider this to be a bug?

Well, i meant, that when mobile data is on and no wifi then cannot enter servers. But via wifi it is possible.