So far the only SVG elements that we have found to be an issue are clip-paths and patterns.
If using clip-paths, open the SVG in your editor and actually crop the images down the size needed manually. This will have the added bonus reducing the file size of the SVG.
Render patterns as individual elements or apply a crop to the image manually if using a pattern to crop an image.
Also be sure that your SVGs do not have links to images but instead have the dataURL added directly into the SVG so that anyone viewing the resulting proof does not have to have an internet connection to view the proof. If you must have an image link in the SVG, be sure to encode special characters in the url in the SVG properties. Also having a link to an image in the SVG will prevent the Instant Proofer from being able to export the proof due to the built in security of your browser preventing outside URLs.