Unable to Export Table Mapping (Database Replication)

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We are facing an error while trying to export previously created Table Mappings. The error itself: Exporting an empty object is not allowed when element is neither optional nor nillable (http://www.mendix.com/:TableMappingList|TableMappings|ImportCall_TableMapping|ImportCall|ImportRefNr attribute: DatabaseReplication.ImportCall.ImportRefNr) This doesn't happen for the Table Mappings which I've just created, export works without any issues. I went though older mappings which I tried to export with this error and it doesn't seems any data are missing. The mappings were created while we were running App on v. 7.23, nowadays we runs on most recent 8.1.1 Did anyone have a similar error or does anyone know the solution?  
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