Minecraft Realm Keeps Getting Corrupted

I've been playing on a realm with my two brothers, our little cousin and my girlfriend for a couple of weeks now. Since yesterday the game started to corrupt very frequently, which always returned me to the same backup, where I was exploring in the Nether. I come back to my house and not so long after roaming by my base the game says it got corrupt. I reload the backup save I had and the same thing keeps happening: shortly after leaving the nether, putting my stuff in my chests and leaving to explore the overworld, whether it is to find villages, new biomes or to mine nearby, the game corrupts after 20, 30 minutes. I always come back to that same point where I'm about to leave the Nether, on the same save.

My realms world has less than 70 MB. It doesn't look heavy to me. We all play on our iPhones and had no previous problems to that. I don't think Internet connection is our problem, since I've tried both with wi-fi and my own phone's 4G, which is a fairly decent as well. With both connections I've experienced the same problem.

I don't know what to do... please help us!