Export PDF/PNG doesn't add image to the downloaded PDF/PNG

Currently, I am using diagram v5.0.1 and while I download PDF/PNG, no image is added to the downloaded result. I have gone through the docs thoroughly but I don’t know for some reason the picture just doesn’t come in the PDF/PNG.

Could you please, provide a complete demo or a demo link, where the problem can be reconstructed locally, as the following snippet seems to work well for me: