Also to inform you all that Dashed boundaries with different Colors did not work with Mathematica’s ExportString [ ] and I am sure there is a way to solve that, and I am going to write to techsupport about.
Seemingly if I Export from the grammar and then APIFunction on the Wolfram Cloud there are differences to the output String than if directly Export from my desktop into a file.
This we have seen many times and always found a workaround.
It is a flaw which Wolfram over the years has done a good job addressing but still some leftovers here and there.
Well, you can take Observable out of the picture easily enough by just opening the URL in a web browser. If the resulting string is not a complete SVG, then you’ve got your culprit.