Embedded reports in Dynamics365 dashboard not logging in

Thanks for all your suggestions. 

I can confirm that I have added the user as a Member to the workspace - although I don't really want to do this as I don't want to share the workspace, just the report, but have done this for testng purposes.

I have also cleared the cache numerous times, including emptying the cache and doing a hard refresh.  I can click the Open in PowerBI button, and the report and the workspace opens without any problems, BUT, it still will not appear within the Dynamics dashboard and the image below appears with 'Authentication wasn't successful'. 

Again, if I open a new browser window as a Guest user, log in with the same account and re-authenticate (2FA) the dashboard automatically logs me in and displays correctly. It is obviously something to do with caching while logged into Edge with an account, but cannot figure out the fix. As most of our users all have Edge accounts, I need to be able to find the problem before we can deploy this out. 

Just for clarity I am using the New+  -> Dashboard  -> PowerBI embedded feature and selecting report from within the new unified interface Powerapps Maker admin centre, not using Iframe within a dashboard or creating a webresource html page. 

Any other ideas?