Maybe it doesn't have an official name or anything, I just mean the screen where you're writing the expression.
But if it's working in Field Maps, then it may be an issue specific to WAB. Using your same expression, I get this in a web map:
But when I go to open the Attribute Table widget in WAB, it hangs, just as you're experiencing. Interestingly, I see the same issue even in the Map Viewer's attribute table:
I don't think there's anything wrong with your code, but something about the expression and how the table is trying to interpret it. It may be a bug, or perhaps a limitation of some sort. I've tested a few alternate methods, but cannot get the lat/lon values to populate the table.
- Josh Carlson
Kendall County GIS