https://userapps.support.sap.com/sap/support/knowledge/en/3563451
3563451 - Group Reporting: Selecting Measure: 'Quantity' with Period Mode: 'YTD' in the Define...
In the Define Validation Rules app (App ID: F2627), for a validation rule, in the rule expression, you are trying to select the Measure: 'Quantity' with Period...