Probably tied to intermittent performance issues with ArcGIS Online as noted on the health dashboard?
https://status.arcgis.com/
If data loading errors occurs I recommend:
- Checking the health dashboard or ArcGIS Online home page for system maintenance
- Attempting to load the Hosted Feature layer from its Item Details page in a new map
- Sanity checking - are you the owner? Do you still have shared access? Was the data always not loading, is it intermittent?
There are loads of reasons a layer will fail to load in a map or survey123. Unshared, deleted, corrupted (e.g. csv upload with bad data). There are a lot less reasons a layer you own will fail to load intermittently when it has been working for sometime with no change. Signing in as the owner and adding it to a new map and then refreshing the page is the fastest way to check the nature of the issue and go from there.
If you suspect a service disruption, get as much detail as possible, ideally a publicly accessible impacted service URL and contact technical support.