After going through the normal sequence of getting to take-off, the controller and 2s don't see each other. No handshake. I fiddle with turning off the controller, and then the drone and reloading the app, etc., and eventually it links and everything is normal. However, yesterday there was no handshake no matter what I did. Batteries are fully charged and there is no software/firmware update notice. Any suggestions as what I should try now?