Map not loading in Map Viewer which is in turn not Loading in Dashboard

[AndrewCastilloTBSL]

A friend of mine is having a weird issue.

When he opens his map on Map Viewer it does seem to load but when he switches to Map Viewer Classic it shows this message despite not loading when it first opened it Map Viewer.

and this in turn leaves his Dashboard blank because his map on Map Viewer doesn't seem to load.

According to my friend he said he created the map, but the data owned by him 

Is this a technical bug, or it has something to do with access to the layer he wants to use?

[rcGIS]

Hello @AndrewCastilloTBSL,

Have you checked the browser dev tools (console & network tabs) to see if you can find additional information?

Could it be related to the layer data types (context)?

This recent Esri Community post might also be helpful; the user who posted it encountered the same error message.