Recently I ran across a deprecated license migration scenario within O365. To simplify the environment, group-based licensing was used on all users with automated assignment (required AzureAD Basic or higher).
The above looks good, except the migration never finished. The main O365 portal page would be stuck at this screen and never complete the migration. The solution was to manually go out to the Azure AD portal (https://portal.azure.com) and manually create/delete the required license changes. Once the license assignment changes were complete, the main O365 Dashboard was available once again.