This happens occasionally and I don't know what the fix is. Illustrator cannot properly display certain SVG files that look fine in a brower and Inskscape, and validate with no errors.
For example, this file of a heraldic crown from Wikipedia Commons appears fine when I open it in Inkscape, but Illustrator goes nuts. I'm using Illustrator CC 2015 on Mac. This is how it displays in Illustrator:
This particular file had some hidden shields outside the artboard, but I deleted them, and no change. I removed unused defs, tried saving as plain SVG, etc but still Illustrator freaks out trying to display it. I've had this happen before - sometimes the entire artboard goes gray, and while you can select elements, you can't actually see them. Copy/paste into another document brings over the same problems. Sorry if this has been I've tried searching for answers but didn't find anything. Thanks.