I am working with arcade expressions for a popup window and after only getting the error below I realized something else might be going on. Also I notice that no Global variables are available in the expressions reference pane?!
This is the error I get for any simple function...
Execution Error:Cannot read property 'root' of null
I have no problem doing this in other maps.
I am working with a simple "Parks" point layer, and the map service and feature service have the same result.
Here is the AGOL item
https://orangeville.maps.arcgis.com/home/item.html?id=9bdcb27048ac484bb6a09b2574874640
it just references my AGS map service here
Layer: Parks and Recreation Areas (ID: 0)
and here is the feature service of the same ()
Layer: Parks and Recreation Areas (ID: 0)

Please help me figure this out, I'd like to build my popup with arcade expressions
UPDATE 1: The error in firefox is Execution Error:e._profileGlobals is null (a little more helpful perhaps?!)
UPDATE 2: I uploaded the feature class to AGOL hosted and still the same? here is the AGOL hosted item.
https://orangeville.maps.arcgis.com/home/item.html?id=887861850a3c402dae4f3ac8bff88e1f