I have had this happen on a lot of my contact sensors V2. For example, I received a low battery email this morning and the contact was at 22%. I replaced the battery and the contact forgot it was even paired to my system. It isn’t just one that does this, it seems they all do it when you remove the battery. Any reason I am losing my contact sensor’s pairing from just swapping batteries? They were paired working a foot or so of the hub a while back but when the battery is pulled, so is the pairing.