Why would it read twice?

UnPivot works for this

Create Table #Test (Id Int, DtCont1 char(8), DtCont2 char(8), DtCont3 char(8))

Insert #Test (Id, DtCont1, DtCont2, DtCont3) Values (1, '20180229', '20180330', '20180428')


SELECT Id, DtCont
FROM #Test
UNPIVOT
(
DtCont
FOR...