Matt J. Not a shit answer at all, I get it must be frustrating not knowing what's triggering it. But what I can tell you is that there seems to be a difference between Copy for Webflow via icons.relume.io and pasting the svg as code. The copy for webflow works great, and pasting svg code from figma doesn't, even when I first paste the svg through the transformer on icons.relume.io.
Copy for figma, paste it in figma and then trying to pase it in webflow and the error occurs again.
Copy for webflow, paste it in webflow, then copying the embed code from webflow and paste it in webflow again and the error occurs.
Seems like a really odd and hard issue.