KiCad lets traces go down to the board trace_min, but the Specctra export only carries net class widths, so Freerouting never learns about it. On 848 of 1,142 PCBench fixtures, trace_min is below the Default class width, and 100 of the 138 boards that failed to fully route are among them, for example a board with 254 um traces in a 508 um class.