I thought I’d throw this into the group. After months of suffering from an occasional bug where people’s Citrix sessions seem to freeze I have been able to deduce the cause down to something related to the gpu acceleration. If I for instance edit one of the Vmware VDA machines and remove the gpu this problem does not happen at all anymore on that server. It also only happens when the user uses his Citrix Xenapp session in “Maximized” mode. The combination of these 2 factors seem to trigger it.
Also interesting to note is that whenever the screen at the end user laptop or pc seems to freeze (like a glass screen you see a frozen picture of the current/latest screenrefresh) there is in reality no problem on the backend VDA server. The session never froze there or showed any hickup or error. As such a simple confirmed workaround is disconnect+reconnect to the session.
So in summary this mystery feels like the Citrix is trying to switch codec or something similar in order to activate gpu acceleration and freezed at that point.
ps: of course I have opened a Citrix case as well but I thought I would work both fronts as people here might have this problem too or recognise it.