You can only pair it once to the device.
If I flash a new rom on my Mix2 android wear won't see the device as it's paired to the old Rom.
You have to reset the android watch (Factory reset).
Then it will appear in the android wear app.
It's annoying I know.
I saw that the android wear app does not ask me to activate geolocation even if it has all the permissions maybe that's why I do not find the watch, I do not know if it is a bug of the rom