hello
i am updated for this problem in debian 8.9 server with yunohost
[quote]
W: Erreur de GPG : http://repo.yunohost.org jessie InRelease : Les signatures suivantes n’ont pas pu être vérifiées car la clé publique n’est pas disponible : NO_PUBKEY 360AAF3259A3E6FF
it’s a ~known issue that some people encounter on their server … We’re not sure exactly why at the moment (because everything looks alright when we try to investigate it, so it’s not clear what’s wrong…)
If you trust your machine, your network and the Yunohost team though, you can bypass the issue by running apt-get update --allow-unauthenticated … Sorry not to be able to propose a better fix