Web map dispalys in map viewer classic but not map viewer

[AndyMcEvoy]

I created a map in Arc Pro v3.3 and uploaded the map to my AGOL content. In AGOL, the web map opens fine in map viewer classic - all the layers display as expected. But, the map will not display in map viewer. There's no error message, the map viewer page opens but stays blank.

Any ideas?

[RussRoberts]

Can you share the web map and I can see if there are any errors in the dev console.