Something’s rotten in Denmark…
I have reduced your file down to the bare minimum - just the symbol - set to persistent - with the enclosed image; all code and ancillary files are removed. A mouse click on the image to change scenes.
The symbol disappears as the background is transitioning (what ever the transition style) in the four major browsers; however, if the symbol type is set to standard all works as expected.
I have also started completely from scratch. As soon as the new symbol is converted to persistent, the result is as before.
Project file (set to persistent): Heuristic_6-JHSv1.hype.zip (458.4 KB)