Message box function works fine on Windows 10, but it does not work on a citrix server with Windows Server 2016.
The cause could be either due to update of the server or an intermittent error.
Release : 8.6
Component : Gen Run Time, GUI
It could be due to environment problem.
1a. On Citrix, run the application in trace using DTU to confirm that the Message Box code gets executed.
b. Check the Taskbar in case the Message box is being displayed minimized there.
c. Check for any messages in the Windows Event Viewer section "Windows logs > Application"
2. Install new Gen 8.63 Consolidation PTF WKS86300/LU06327 which rolls up all fixes since WKS86200, then regenerate/rebuild the application.
After doing this on Windows 10 and copying the built Gen applications and runtimes to Citrix the problem on Citrix was resolved