Unable to add field to hosted feature layer, possible causes?

[KGalluccio]

I have a hosted feature layer which I am unable to add a field.  In AGOL>Data>Fields, the add field button is not available.  If I open the feature layer in Pro, add the field and try to save, I get an error "Unresolved errors found in *Fields: <feature layer name>.

I know that if the hosted feature layer has a joined view you cannot add additional fields.
I have deleted all of the joins, (total of 2), and permanently deleted them from the recycle bin, yet the Add Fields button is still not available.

What other reasons would cause the Add Field button in a hosted feature service to be available?

Link to hosted layer:

Albany County Tax Parcels 2024 - Overview

[KGalluccio · Accepted solution]

Support was able to resolve this issue.  Somehow this feature layer still had some "ghost" views associated to it.  I had deleted all of the views that were created from the feature layer yet when I viewed the REST Services Directory, layers details page>click view next to URL on bottom right.  Here it was showing views associated to the feature layer.  When clicking on the view, it could not be found.

ESRI had to remove the "View" on their end to fix the issue.

Not sure how this happened.  The views were created from the details page of the feature layer, using the Create View Layer option.  The views were also deleted within AGOL and permanently deleted from the recycle bin.

[AustinAverill]

I figured this is what was happening when that previous script didn't work.