Possibly this happened after Office 365 update when users offered by Outlook to compose new emails using Edge Browser,

Now when they access eg Contacts in Dynamics 365 within Outlook, using older Add-in for Outlook, they are redirected to Edge which just shows CRM login page, not the contact page requested. Sometimes IE shows a page in the foreground saying 'this page best viewed in Microsoft Edge'

Even if users login at the page presented in Edge, no Contact or other CRM page is shown.

Other users still opening Contacts in IE and having no problems.

It makes no difference in Default Apps what you set the default browser to, nor if you set browsers in Defaults by file type or protocol.

Server is on premise but hosted in the cloud and is version 8.2.27

Clients are 8.2.0005.0004

It says We recommend viewing this page in Microsoft Edge