Data vanishes after a split second!Urgent help

I suggest you work through it bit by bit. Forums are not really suitable for "urgent" help.

1) Move all the code that you have under RETURN, to be placed above the RETURN and put it into it's own variable.

2) Then under the RETURN  put firm_userprincipalname to make sure it has a valid value (test it in a table visual or something). If it doesn't, then it'll find no rows in the rst of the code and you'll just get a zero result.

3) Maybe even comment out one line ata time in the filters of the CALCULATE(), until you start getting some values. This will help narrow down which filter is hiding all your rows.

Code formatted

AvgFIRM_SellingPrice =
VAR firm_userprincipalname = [MF_USERPRINCIPALNAME]
RETURN
    CALCULATE (
        AVERAGE ( IMPORT_SQL_monthly[SellingPrice] ),
        OR (
            IMPORT_SQL_monthly[CurrentStatus] = "Sold",
            IMPORT_SQL_monthly[CurrentStatus] = "SaleComplete"
        ),
        TBL_CALENDAR_periods[Value] = "This year",
        LOOKUP_MF_USERS[PrincipalName] = firm_userprincipalname,
        IMPORT_SQL_monthly[PartShare] = 0,
        USERELATIONSHIP ( IMPORT_SQL_monthly[DateSold], TBL_CALENDAR_date[Date] ),
        USERELATIONSHIP ( IMPORT_SQL_monthly[MemberFirm], LOOKUP_MF_USERS[firm] )
    ) + 0