I was having an issue where some of the objects in my SVG were not rendering in Ignition and others were. I tried opening the SVGs in a web browser also and the same objects were not visible.
The fix (in Inkscape) was to select the objects that were not showing up and convert them from objects to paths. (Path/Object to Path or SHIFT + CTRL + C).
I was able to select groups of objects and fix them like this.
Just passing it on in case someone else encounters this issue with custom graphics. I feel like this is an inkscape problem rather than an Ignition problem but I know a lot of us use Inkscape for custom graphics.