Below link which is something relevant(not 100%) to your issue to give you some ideas:
Coming to your original issue: Why it happens:
Point 1: RF pollution in your WiFi network, May be internal or external from known and unknown source. this issue may trigger the devices to roam frequently for better performing AP.
How do i check this? Start with some basic tools as follows:
Download insidder - http://www.metageek.net/support/downl...
this will tell you about all wifi networks in your area and give you channel wise graph to tell which one is less or more congested. will help in channel planning too.
Look at stats here - http://prntscr.com/4iv4vd
point 2: if not because of point 1 then your laptop on which citrix is installed are on the edge of the wireless network hence poor connectivity. See if you can bring real close to the AP and see if they see a change in performce. This is just for testing.
Some suggestions: take a look at the logs which is being printed out in ZD and scrub it with problematic Laptop mac add to see what it has been doing all day so that it gives you pointer about possible root cause and suspect AP.
Keep ZD Upto date on firmware. check with support for best one.
Also make sure that devices on which citrix is running, their WNIC is also upto date on drivers.
---Please post here make n model of WNIC on the laptop/device running citrix.
---ZD Firmware version to suggest upgrade or not
---Since when are you seeing this issue, did you update anything on controller post which you are seeing this? anything got changed somewhere else which you may know?
Hope this helps.