The individual elements of the List need to be separated with a comma and not an &
see the comma at the end of each line
List("; ",
If (not Contains([Quality Approval], $QTA & "] Approved") and not Contains([Quality Approval], $QTA & "] Rejected"), $QTA) ,
If (not Contains([Quality Approval], $QTB & "] Approved") and not Contains([Quality Approval], $QTB & "] Rejected"), $QTB) ,
If (not Contains([Quality Approval], $QTC & "] Approved") and not Contains([Quality Approval], $QTC & "] Rejected"), $QTC) ,
If (not Contains([Quality Approval], $QTD & "] Approved") and not Contains([Quality Approval], $QTD & "] Rejected"), $QTD) ,