I've just tried the official app, updated to latest version, feed works fine.
I'm guessing this might be because you're on mastodon.social? It's way too overcrowded and this often causes technical problems. You might find other servers are more reliable.
By the way, you don't have to use the official app at all, the third party apps tend to be better. On iOS apps like Ice Cubes, Toot!, Ivory and Mona are good.