In building one of my latest environments on Server 2012 R2 with XenApp 7.6 I noticed a strange phenomenon, when logging in, after the processing of my Group Policies my XenApp session would hang at a black screen for about 10 seconds as seen in the screenshot below:
After wrecking my head disabling GPOs, using Citrix and MSFT Folder Redirection, disabling asynchronous logons and the whole roundabout of troubleshooting steps, it seemed that nothing was working.
I then proceeded to do a trace on the issue and noticed that my logon was being hun by wfshell.exe which is tied to the Citrix session process. It turns out that there is a private hotfix for this issue which is tied to Server 2012 R2 running XenApp sessions. The hotfix is CTX142036.