Scenario – a user who had been working fine can no longer launch a Citrix Win10 non persistent desktop from any client – Windows or Wyse ThinOS, internal or external. No other users affected. No related errors in the event logs on the Delivery Controllers, StoreFront or the clients.
I ended up using Chrome to download the ICA file, opening it and getting the IP address of the desktop that the user was being directed to. NSlookup gave me the name and then I went to the vSphere console of that desktop. When I opened it it was black like someone was logged in via Citrix already, however in Studio it showed no one on it. I rebooted the desktop in question and after that the user was able to log in.
Below is a screen shot of the errors in case anyone else comes across it. All of the other posts I saw talked about firewall ports and Netscaler and none of that was relevant in this particular case.