Hi Jack2006,

Try to put "My_tag1." on Tagprefix, maybe is only that you forget the '.'

jack2006

I create a PLC UDT("MyType") in Project Library by drag and drop it from PLC data type.
Then I create Faceplate("MyFaceplate") that use that PLC UDT.
I create some tags("MyTag1","MyTag2",) of type "MyType" by drag and drop it from data block of PLC.
Faceplate placed on Screen that Displayed in ScreenWindow.
If left Tag Prefix empty on ScreenWindow and  in interface of Faceplate instance write "MyTag1", then all working ok.
If in tag prefix write "MyTag" and in interface of Faceplate instance write "1" nothing is working.
Nothing is working even if in  interface of Faceplate instance write "@NOTP::MyTag1"
What do I wrong? 

 I tried to follow you questions and still unclear as to what you are trying to do. If you really want help follow these instructions.

Link

I created Faceplate with using PLC UDT as input data for industrial objects (pumps, valves ...)

I created "dialog boxes" for this objects. This dialog boxes Displayed in screewindow with tag prefix, then not necessary create separate dialog box for every object. Faceplate instances placed on main screen and on dialog box. On main screet tey work, but in dialog box they work only if left 'Tag prefix' empty and in Faceplate instance write full path of tag.

I created test project to demonstrate that issue. FaceplateUDT.jpg need to rename to FaceplateUDT.zap15.

In this project all three instances of faceplate must bee the same. But where used tag prefix this is not work - tag not connected to faceplate instance. 

It looks like it doesn't work with PLC Data Type and you will need to use HMI User Data Type and make sure you check WinCC Runtime Professional when you're creating it.

Follow this example for all the details.

I already rebuild my Project to avoid this issue.