Arg, this got me again! That was my problem too. Had the same issue with the Fibaro sensor-- was paired with S0 and flaky. Re-paired with Z-stick w/o security and problems went away.
@bobbyD @bcopeland feature request:
I get that HE can't pair w/o security when S0 is available. But how about a pop up warning that the device is/is about to be included with S0?
