The following error message may be displayed on migration to cloud.
This is due to a known bug , where the last state of any page with restrictions is not correctly migrated by the Atlassian Migration Assistant.
Once we fix the bug (that is dependent on the further development of the Atlassian Cloud platform) and notify you of the release, you will need to re-run the migration for this space again. In the meantime please see the workaround below for this bug.
Solution
A workaround you can use right now is to remove the restrictions from the server instance before migrating.