I am using humanistic theme and draggable dialog boxes are not working as expected. I was unable to replicate this error on your demo. The generated code indicates the draggable is set to true as well. Draggable dialog boxes are still working for me with standard theme, but those are the only themes I have tested.
Just tried the demo and indeed it worked normally on my end using Chrome:
Not sure what caused the issue but I changed the theme of my project then reverted it back to humanstic and now everything is working as expected.
Thank you for the reply!