At the very least, an option to not run the optimizer (sanitizer is fine, there is nothing to sanitize in that svg anyway) would be useful so could at least not break things.
It looks like it is removing the gaussian blur filters while the links ‘to’ those filters remain.
Manually adding the missing feGaussianBlur's back in fixes it and the SVG properly reappears.
Further testing shows that removing the filter attributes from the path’s also fixes it (though doesn’t look quite perfect due to the missing slight blur).
So as it stands, discourse is removing the gaussian blur filter elements while leaving the named references to them in the rest of the nodes. Discourse needs to either not remove the filter nodes that contains elements that are not script-issues (gaussian blur is not) or it needs to remove the associated attributes that are referencing the now missing filter elements. Leaving it in this half-state is broken.