I'm guessing it's something in the internal XML coding of the PCB svg, but I'm not smart enough to work that out.
I drew another rough one from scratch that's not dimensionally accurate and works fine, so it must be something in your PCB svg.
Here is the rough one so you can look at the XML structure.
Silkscreen at the top.
copper1 (top laver) with the pads .
copper0 (bottom laver) inside copper1 and empty.
Group all of those in a group called pcb
Just change the .fz extension to .svg
drawing-1.fz (18.6 KB)
I suggest doing another clean one or mod-ing mine and making it dimensionally accurate.