Most vector formats (including both SVG and PDF) support two different rules for how to fill an object, the even-odd rule and the nonzero rule. Here’s a description of how the fill rules work: Understanding the SVG fill-rule Property — SitePoint
The Glowforge software only supports the nonzero rule in SVG files. In PDF files it supports both rules (even-odd and nonzero) so you may be able to fix your problem by converting the file to PDF before uploading it.
I first discovered this bug back in 2017. I used to report it annually but I gave up after a few years. Here’s one of our past discussions on the topic: Glowforge still doesn't support the even-odd fill rule in SVG files as of January 2020