Embedded Map displays with AGOL but not our Portal

[TychoGranville]

I use the same Map Image Layer (and basemaps) to create a web map then copy the code to embed it. The AGOL version works on a web page, the one hosted on our Enterprise does not (it comes up blank, neither layer nor basemap drawing). We have a number of public and private apps that function as they should, this is the first time I've tried an embedded map. The documentation (Embed maps, apps, and groups—ArcGIS Online Help | Documentation ) is pretty  straightforward, not using AGOL has tech support stumped. Any ideas?

Thanks,

Tycho

[MatthewDobson]

Is it a permission issue?? User types, roles, and privileges

[TychoGranville]

It feels like a permissions error, but I can't tell where. I'm using the account that is used for all of our public-facing apps on our Portal. I'll try a different admin-level account and see if that works as a test... back soon.

6/25/2020: Nope, didn't work.

7/9/2020: Figured out why it didn't work, fix will be long term with our IT staff. In sum,

Embedded web map hosted on our Portal (not the one on ArcOnline) fails to display in FireFox and IE. (Chrome is fine *). IE does not show an error, FireFox logs (only fatal errors shown):
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Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://machine and port/arcgis/rest/info?f=json. (Reason: CORS request did not succeed).

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://machine and port/arcgis/rest/info?f=json. (Reason: CORS request did not succeed).
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* Chrome does not work if accessed through VPN/TeamView. We found an error like this accessing ArcMap awhile back, apparently it affects Portal as well.