Yeah, that's unfortunately not something that we can fix. Various apps read SVG files differently from each other, so we can only maintain compatibility with Illustrator, Inkscape, and web browsers. Even with those two 'pro' apps (Inkscape and Illustrator), we have to tailor the output file to maintain the best output possible while accommodating each apps' quirks when reading SVGs.
Edit: We won't say that Affinity Design compatibility is out of the picture forever, it's just that now we haven't investigated the quirks of the app enough to find out what workarounds that we can use to make our SVG files imported correctly.