Configuring popups in HTML mode in ArcGIS Pro will not be honored when used in Web App Builder. The solution (found here ) is to configure the popup in Map Viewer Classic.
HOWEVER, if I have to republish the web layer from ArcGIS Pro, I am told that it will wipe out any configured popups that I created in Map Viewer Classic.
I suggest that Web App Builder be programmed to honor the HTML mode popups created in ArcGIS Pro.
