I ran into this issue recently on Windows 7 PVS target devices. The Citrix Receiver 4.3 would spin for a long time and finally give the error “Cannot connect to server”. This was a newly built XenDesktop 7.6 FP3 site with Windows 7 PVS 7.6 SP1 target devices, and Storefront 3.01. The interesting thing was this was only happening on the Windows 7 PVS devices. From every other device, we could connect to the Store just fine using Receiver. There was a slight improvement when we turned off the Receiver Unified Experience, but connecting to the Store and App enumeration was extremely slow. I also tried the latest Receiver 4.4 and earlier 4.2, but got the same result.
I spent a significant amount of time troubleshooting this, and even opened a ticket with Citrix support. In the end, I was troubleshooting a slow Internet browsing issue, and on a whim unchecked the Internet Explorer setting under Tools>Internet Options>Connections>LAN Settings>Automatically Detect Settings.
Immediately the Citrix Receiver started working normally! Another issue that we had been having on these Desktop VDA’s was that Outlook 2013 was super slow to load. After making the above change, the problem with Outlook was also resolved!
After experiencing this, I googled again more specifically this time, and ran into this blog post https://davidrfigueroa.wordpress.com/2015/04/08/receiver-4-x-login-speeds/. So obviously others have ran into this issue before. I hope that Citrix adds a CTX article about this issue, as it was a difficult one to track down!