Sync not working on iOS app

When I open the iOS app, a "Syncing data..." banner appears at the bottom of the screen. After about 10 seconds, the banner disappears, but the data is not actually synced at all. Tasks and events added from other devices are completely invisible in the iOS app, and tasks I mark as complete in the iOS app still show as incomplete on other devices. I'm running the latest version (v1.71.7) on iOS, and sync works perfectly fine on macOS and the web version, which are also up to date.

This issue didn't occur until yesterday, so I may have accidentally done something wrong, but I can't think of what it might be. Since the iOS app is currently not very usable, I'd appreciate any help.