One thing could always be that the security settings aren´t set properly. Then Mendix tries to retrieve data from the database, but is prohibited by for instance entity access not being set properly. In my experience this doesn´t give feedback to the end/user that rights aren´t set properly and results in the progressbar appearing and the page continuoulsy looking like it is loading.
Are there maybe extra modules/MF's added / modules/MF's renamed during the migration?