Client Windows OS display resolution would be changed when using Citrix Workspace App.
From CDF trace, there is not any action to change the client display resolution:

From process monitor log, the client display resolution was changed by selfservice.exe:


Furthermore, it's identified that selfservices.exe was injected by a 3rd part software named ' Sangfor'.

Problem Cause

Workspace app natively would not change the display resolution of the client.
It's caused by the 3rd part software 'Sangfor' injected into the workspace process interfering the system action.