ArcGIS Online is experiencing intermittent issues today. Esri is aware of the problem and is working on it. You can check the status at https://status.arcgis.com/. 

This may impact any apps, web maps or services you have published through ArcGIS Online. In addition this could impact the use of apps such as Collector, Survey123 and QuickCapture. It may also cause some issues with ArcGIS Pro LIcensing.