I am on Enterprise 10.9.1 with a 25MB polygon layer.
In the old map viewer it takes half the time to load the map compared to the new map viewer.
The old Map Viewer first draws the layer and then the basemap.
The new Map Viewer first draws the basemap and then the layer.
What is the cause and how to resolve it?
My initial guess was that it is related to introduction of vector tiles, creating more load on the client side on the CPU (since there is no dedicated GPU).
There seems to be a difference in the Basemap when changing between old and new map viewer (labels are placed differently). But checking the URLs, they seem to stay identical. Only the order in which they are called changed.