I’ve experienced this a few times. Removing the app by swiping up in the recents screen and then restarting it has fixed it until now, but today that’s not helping anymore; when I reopen the app, I still get the outdated content. I’m not aware of a way to properly force-close an app, like you can on Android, so I don’t know what else I could try.
An easy way to address this quickly would be to add a manual refresh button to app itself.
