This is most likely a common issue with hosted feature layers published from ArcMap vs other channels of publishing. The layer in question was published several years ago. The features display on the previously published webmap but when trying to backtrack the source of the data, I come up empty.
The description for the feature layer is greyed out.

The item details are not hyperlinked from the source map content and are greyed out, whereas other layers in the map are hyperlinked to their details.

Could this be a compatibility issue with the push to publish everything from Pro? A permissions issue? How is it that I can see the features from the feature layer?