Z-Wave device id: 7 failed S2 bootstrapping - KEX_FAIL_KEX_KEY: Key failure indicating that no match exists between requested/granted keys in the network. - the device needs to be excluded then included again to use securely.
I think it just looks a bit ominous...but I am purposely adding without security.
What type of device are you adding? I have no security on any of my devices and I don't recall ever seeing this message.
However I don't have any door locks which might balk at adding without security.