@afterspencer Hi and welcome to the forum 
Likely a firewall in the way, or not resolving, or the nodots entry.
I had to shell into my test instance and then edit /etc/resolv.conf to add my local DNS servers… Then select the three repositories and refresh…
More info here: https://ranchermanager.docs.rancher.com/troubleshooting/other-troubleshooting-tips/dns