I have a database view (have attempted with just a query layer as well) that works and has worked in the past to display a custom popup in AGOL and Enterprise. This layer now won't display the popup in the new map viewer or in dashboards. If I switch to the Classic map viewer, the popup displays without issue. Also, if I publish the layer as a hosted service on AGOL it also works fine. Seems to only be when it is dynamic from our SDE and in the new map viewer.
I've attached 3 images. popup shows what it looks like in Classic Viewer. popup2 shows that when configuring it in the new map viewer, it will display, but if you click on any of the points on the map, no popup displays. poup3 shows a details widget in dashboards showing No Data.