Migration failed with the following error:
Failed to find source database server for MSSQL database 'mssql'.
Database content will not be transferred to the target panel.
Most probably that is caused by inconsistency on the source panel.
1) Database actually exists in the source panel.
2) Database actually exists on the source database server.
3) The database server 'MSSQLSERVER' is registered in the source panel.
Resolve the inconsistency on the source server if any, or copy database manually, or ignore that message
if database does not actually exist on source.
Objects which describe MS SQL databases were duplicated in Plesk Migrator dump, as a result, Plesk Migrator tries to restore these objects twice. This is Plesk Migrator bug with ID PMT-3830 which is planned to be fixed in future Plesk updates.
The error can be ignored.