Endless spinner in Copilot Sales Outlook App after login to Salesforce

We are experiencing an issue with the Copilot Sales App in Outlook.

Users are launching the app and authenticate to Salesforce successfully.

Then, a message saying "Sales is loading..." is shown with a spinner and nothing happens, no matter how long you wait.

This only happens to some users and not to all users.

Sometimes it happens to users who were previously able to load the app fine.