Cannot export data from expected dataset in relationship situation

Hi Coolpearl Could you try these please 

• Use Fields Only from the "Many" Dataset: Ensure your visual includes columns from the "many" dataset, not the "one" dataset.

• Create a Merged Table: Use Power Query or DAX to merge the "many" and "one" datasets into a single table and use it for your visual.

• Export Underlying Data: Choose the "Underlying data" export option to ensure raw data from the "many" side is included.

• Adjust Relationships: Verify your concatenation key (flag + employee_id) is correctly set up and unique on the "one" side.
  Another way would be to create a calculated table in DAX and use that in a vsiual and export that something like this

ExportTable = 
SELECTCOLUMNS(
    FILTER(
        RELATEDTABLE('ManyDataset'),
        'ManyDataset'[Condition] = TRUE
    ),
    "Employee ID", 'ManyDataset'[EmployeeID],
    "Flag", 'ManyDataset'[Flag],
    "Other Field", 'ManyDataset'[OtherField]
)

If this post helped please do give a kudos and accept this as a solution
Thanks In Advance