I've just a bit more of a dig into this, and bisected my failing file a few times to figure out what was going wrong.
The thing it seems to choke on is this:
<polygon slic3r:type="contour" class="st0" points="-1.8,579 -1.8,579.1 -1.8,579.8 -1.8,580 -1.8,580 -1.8,580 -1.9,580 -2,580
-2,579.4 -2,579.1 -1.9,579 ">
And the particular problem this seems to hold is that
points="-1.8,579 ... "
If I changing that to a positive number (1.8 vs -1.8) then it loads the SVG ok. When Geomerative looks at that string of characters, it sees the '-' and then looks to the character _before_ it to see if it's an 'E' (for some reason - to check if it's using scientific notation maybe?!), but because it is the first character in the string, there _is_ no character before, and so the crash happens because it looks for a character at an index that doesn't exist.
I did a search in my input SVG for points="- to find these lines. I had two of them in a 475,000 line file! These two I could simply snip out and nobody would notice. If you have a larger number, then you can't just snip them out easily!
I've submitted an issue to Geomerative (https://github.com/rikrd/geomerative/issues/9) and offered to supply a fix. In the meantime, you could try my "fixed" version of geomerative.jar here: https://drive.google.com/file/d/1QBjl_QO5te1FfekyODjlsvcbYOFY1kmD/view?usp=sharing
This should go into your processing sketchbook/libraries/geomerative/library/ folder. Move the geomerative.jar that is already there someplace safe and put this one there instead.
This particular problem may not be the only one that causes problems when loading though! But give it a shot.