iCloud documents stuck at 0% uploaded on iPhone

iCloud documents have gotten stuck 2 or 3 times at 0% uploaded on iPhone, maybe because it's cellular data instead of WiFi connection? Other Internet services are working.


Is there NSFileManager or UIDocument API call that needs to be made. I see the NSFileManager method:


- (BOOL)startDownloadingUbiquitousItemAtURL:(NSURL *)url error:(NSError * _Nullable *)error;


Is there a similar method to start uploading a newly created iCloud document in the iOS app?


Normally iCloud syncing does work, but 2 or 3 times lately it got stuck. The problem persisted even after restarting the iPhone iOS. It also does not see new changes made to iCloud documents in the macOS version of the app. Restarted macOS as well. Stuck.


Then on WiFi, later the same day, the sync just works. Why the hangup?