@Ioan Scott yes I have, my WiFi has two bands, I've tried both, only difference is one causes a disconnect within ~5 seconds, the other causes a disconnect within ~30 seconds.
Yes, the Unable to Connect to World can be solved by closing MCPE and reopening, then trying to rejoin, if it occurs. Usually though I get disconnected, and can rejoin immediately, only to be disconnected ~30 seconds after joining yet again.
I've also noticed that if you try to build or chat, it will disconnect you sooner.