I’ve tried the demo code and see that the feature Editor doesn’t work properly same as the one on your demo site does.
I opened a same visio file and it’s rendered differently on Demo site and local demo code. Please see the attached images below
image (1).png (221.0 KB)
image (2).png (190.0 KB)
This is the visio file I used in this test
Test-Diagram.zip (583.4 KB)
This scenario is reproduced at our end. Hence, we have logged it in our internal issue tracking system with ID DIAGRAMAPP-204. You’ll be notified as there’s any update.
Upon further investigation, it’s been observed that this is API limitation because you are evaluating the API in trial mode (as we can see the evaluation watermark in the browser output). Please apply a valid API license and you will not face this issue. You can avail a temporary license here in the purchase wizard. Learn more about API evaluation limitations here.