When you say the rest of the project, do you have controls such as a BasicLabel showing values from TwinCAT? If so, the read should work because behind the scenes they use the same me BeginRead to retrieve values.
Do you have TwinCAT installed on the PC you are running the AdvancedHMI application? If so, that could be causing some issues. It does with TwinCAT 2, but I never tested it with TwinCAT 3 to see if it has the same bug in the AMS Router,