Pop-ups configured in ArcGIS Pro change when the feature service is added into a new Map Viewer?

[Hayley]

I have published a feature layer (non-versioned, just a copy) into ArcGIS Enterprise 10.9.1. The pop-ups were configured in ArcGIS Pro before publishing. 

When I check the pop-ups in the Visualisation tab of the published layer, they have honoured what I configured in Pro.

However, when I add the feature layer using the service URL into a blank web map in the new Map Viewer, the pop-up configuration is lost. The pop-ups stay consistent in Map Viewer Classic. 

I am confused because I configured the pop-ups in Pro. 

How do I get the pop-up configuration to stick in the new Map Viewer when using the service URL?

[DeanMoiler]

Just as an update on this one. We've found there were a couple of bugs logged for this one. The first one is closed as a duplicate, and the second one is in production plan, so fingers crossed we get a solution to this in an upcoming patch.

BUG-000154648 for ArcGIS Pro (esri.com)

BUG-000160273 for ArcGIS Pro (esri.com)

It seems to be a server side / portal side issue with publishing from offline sd, rather than a python/dsc/server/gp tool publishing method, as all SD publishes have the same issue, and overwriting the service directly using pro publishes the "data" component of the map image layer item, that is not published otherwise. Hopefully we'll see something soon.