When attempting to open the Custom Label expression building dialog in the new map viewer, clicking the icon on 1 of the layers does not open it:
For other layers it does open:
Is there something specific to the layer that prohibits this dialog from opening?
Thanks Russell... I'd have to open a premium ticket in order to not show on public forum (which I can do). In the meantime, I can provide dev tools output that may give you some intel to help resolve:
No worries, if you can PM me the JSON of the web map I can see if anything there is causing it but probably will need to checkout the map & layer to look into it. You can invite russell_jsapi into a group with the items shared to it and I can check it out there when you can share the sample.