Thank you for reaching out to us! I'm sorry you're having issues with migrating your apps.
Here are some of the troubleshooting steps we have seen fix previous user issues with loading the migration page:
- Open Google Chrome in an incognito window, and try to open the migration page from there. Or try a different browser entirely.
- If you are on a corp network, please make sure the Fabric domain is whitelisted.
- Enable the developer console in your browser, refresh the migration page and screenshot what errors pop up under the "Network" tab.
- Make sure your browser does not have any popup blockers enabled.
- Make sure you are the admin of your Fabric org, and an owner on the Firebase project you are attempting to migrate to.
Would you also be able to tell me if your org that you're trying to migrate apps for has a very large number of apps?