Serialized Item getting split with 2 quantities in each line

We have a S1 order of serialized item.As expected, quantity on sales order  has got split after print pick slip (R42520) with quantity 2 on some of the lines while the other lines have quantity 1.

Usually, with serialized item we get only 1 quantity on each line. We have not seen such issue in the past.

FYI,we have checked lot process type field F4102.SRCE is set to 7

What other fields should we look into and verify?

Thanks in Advance!