Found another quirk in the Analysis widget today.
If you go from a popup then Set As Analysis input to a tool that uses a field list off that layer works fine.

But if you use the Select widget, select a polygon, then do Set as Analysis input from there, then the field list will not populate at all.

@Wei_Ying I think this is similar to the Search widget issue with the first popup. The tool is getting an input of just # somehow.
We also see that if you have a popup from the last session up and come back later then try Set As Analysis input that will fail also saying the input layer is #. The user must reclick the polygon, get a new popup, then its happy.
I am happy to show the team all these quirks if it will help (I have 10 now I think). This is a AGOL ExB.
thanks a lot