So I was using the latest Proxmox 5.0 beta2 and the web GUI randomly lost connection. I updated the packages and rebooted but got the same behavior again. At that point I just gave up. It was bad enough that out of the box there was no shell prompt on a new Debian 9 container.
Don’t get me wrong, I bet that all of my issues could be resolved or properly reported to further development of the beta but I’m just not invested in Proxmox — XenServer is pretty great for my homelab needs.