Why is SVG scrolling performance so much worse than PNG?
I think this is just some kind of a Chromium bug, I've found this issue on SO, because I started experiencing it as well on Mac. It works OK on Opera for instance.
I don't think anyone here will be able to explain why it's slow if it really is a bug. I've created a Chromium bug, please star it if you want the issue to be fixed soon or learn more https://bugs.chromium.org/p/chromium/issues/detail?id=681611