I converted your bitmap to a png. Size shrinks from 1.3MiB to 56KiB A 30x difference. Gosh.
Graphics on Edge.Cuts must be a single closed outline. No gaps, no double lines, no lines crossing each other. The PCI-Express connectors in KiCad’s default libraries already have lines on edge.Cuts. With such footprints you only draw the outside of the PCB and then snap them to the open endpoints of the existing lines in the footprint.
Recently there was another thread with very similar question: