The one with insufficient resources

A colleague of mine had the opportunity to work on a case recently that had a pretty interesting resolution so I thought I might as well just share it. The client was running a CAG 504 VPX serving a XenDesktop infrastructure. Every now and then, during the login the users were prompted with an error of: Intermittent HTTP 405: page cannot be displayed
Refreshing the page would've displayed the resources.

I will not go into details on this one but after months of troubleshooting Citrix was not able to understand why this happens. We narrowed down to where it happens by analyzing the network traces and other logs from the CAG but simply were unable to get to the WHY.

So we were one day in the office talking about VM resource reservations and how a colleague of ours saw some weird things with a NS VPX that was not given enough "juice" so we decided to go down this route and propose to our client to ensure his CAG VPX VM has at least 500 MHz and 500 MB RAM reserved on the Hypervisor side.
I'm happy to say that the issue never presented itself after that.