currentdate() is already date data type.there is no need of to use todate() again.todate() is required if date object datatype is string. Check for query open date object data type.if it's date then remove to date from there also.
Other than that use format "dd/MM/yyyy" if date type is string.
Or try this.
=if DaysBetween([Query Open Date];CurrentDate())<=10 Then Count([Query Status Name];All) Where([Query Status Name]="Open" And [Marking Group Name]="Site")
Add comment