The package mirror pkg0.cyb.freebsd.org hasn't received updates for most of October. As of Nov 5th it seems to be up-to-date again, but some directories are inaccessible, returning a "403 forbidden" (e.g. http://pkg0.cyb.freebsd.org/FreeBSD:12:amd64/latest/), thus causing errors on the user side when the pkg command uses this mirror.
There's been IPv6 issues for most of October. Updates are being pulled into the mirror since yesterday, but it'll be a while to update.
I don't see the 403 at the moment, but I've restarted all the web services just in case its something I didn't know about.
I've re-enabled this mirror.