I posted this in the HE forum but have not gotten any replies yet. I was trying to pair an Iris plug to ST yesterday and couldn’t get it to work so I gave up. This morning I was looking at my HE device list and I there I found the Iris plug! It got paired with HE for some reason, the last time I used HE for pairing was Monday. Today I tried to pair the Iris plug again with ST but before I did that, I rebooted the HE hub… guess what, the Iris plug was paired with the HE hub again?!
Not sure what to think of it 
Next attempt would be to power down the HE hub while I do my ST pairing or give in and just leave the plug in HE.