This has been a problem for over a year; haven’t been able to find a fix online, only forum complaints. 
I frequently play on a wifi-only iPad. I log into Microsoft Live so that I can track my achievements and purchases, and so that I can play on public servers. 

However, if I then play offline (such as on a car or plane), the game will not load, because it takes an excurciatingly long time for it to realize it can’t log in. 

The only workaround I’ve been able to find is to tether the ipad to my phone’s internet long enough to log out. Then the game will load quickly and I can play with my worlds while offline. 

After getting initially loaded, I can disconnect my internet and have no problems. It’s just the initial login that hangs up if I am logged in and don’t have internet.