these reading do not make sense
First checks are to make sure your subcooling circuit has a solid column of liquid feeding the TEV.
Then make sure your liquid to be subcooled is a solid column.
key point here being (you cannot subcool vapor)
Then your subcooling circuit should have around 10 to 12* superheat (40*SST with a 50* sensible suction pipe temperature)
Your liquid to be subcooled is entering at 66* and should be leaving towards the liquid header at around 50 to 55* sensible pipe temperature.
The readings you provide give me the impression that your subcoolers TEV is leaking through the push rods and into the externally equalized line. Giving you a low superheat reading, with no active heat transfer on your liquid to be subcooled.