I'll think about reporting it, but I want to understand the problem more... I think the part of MediaWiki that is supposed to read the dimensions and generate PNG previews seems to be broken. Wikipedia never allows upload of SVG that is nominally 0 x 0, as far as I know, but probably because it always tries to generate a PNG preview.
It really seems to be an issue on Wikias side: I uploaded some .svgs a while ago which are working completely fine. And I wanted to upload some made around the same time (so with the same program, version etc.), and they now just don't work when uploading.
I made these at the same time (first made the big one, and then deleted parts to create the smaller one). I only uploaded the shield back then because there was no need for the coat of arms, but now ... yeah xD It doesn't work