You may want to try it again now. Even though ESRI's ArcGIS Online Health Dashboard says there are/were no issues this morning (as it almost always does, even where there are serious delay issues), there were some serious delay/time out issues this morning.
I was getting time out errors trying to load newly created (empty) feature layers this morning. Finally started working again about an hour ago.
Though, if they were working in other maps, probably not the issue, but worth a try.
R_