The issue is that the mouse is offset by about 20x20 pixels.
I also have access to another app in Citrix, which has the same problem. This especially goes for users sitting on endpoints with high resolution monitors. After Microsoft released Creators Update, several people are reporting some issues with the mouse pointer inside Citrix (Desktop/seamless apps) appears small.
UPDATE: this issue is resolved as of Citrix Receiver 4.10.
