ptr1337
I had this problem from only one ip that was dynamically assigned by a service I am using, and saw that another poster here got error 304 with pacman as well a couple days ago, so I posted this to inform you.
Support on my side looked into this, and they say it looks like another customer was misusing that ip previously. They will look into this further to see if they can confirm why this happened.
Anyway, it would be interesting to know if you can find out on your side why we are getting error 304 on some ips.