During the deployment of a new Citrix XenApp 7 environment (Windows Server 2012 R2 for both VDA and StoreFront), there has been a strange issue that was nearly impossible to replicate. Sometimes users would call and say their applications were flashing back and forth with a black screen. Upon remoting into their machine I can see that is the case. The only fix I found to get them working again was to log them out and back in, which worked 100% of the time at the cost of them losing any unsaved work.