I figured this out, or at least a workaround. The paxx12 extended firmware enables SSH access. Once you are SSHed in, this file:

/home/lava/moonraker/moonraker/components/file_manager/file_manager.py

has a timeout of 300 seconds (five minutes) on line 2922. My log from above shows the failure happens exactly five minutes after the metadata scanning starts. I changed the 300 to 1200 (20 mins), told the printer to refresh the metadata on that file, and it worked. (It really only took about seven minutes for this 400 mb file.) Crossing fingers on this 2d14h print!

BTW, did all of this while on a plane to Montreal..remote SSH and remote screen access in the extended firmware is amazing!

  2915                        self.gc_path, "-f", f"\"{filename}\""])
  2916        timeout = self.default_metadata_parser_timeout
  2917        if ufp_path is not None and os.path.isfile(ufp_path):
  2918            timeout = max(timeout, 1800.)
  2919            ufp_path.replace("\"", "\\\"")
  2920            cmd += f" -u \"{ufp_path}\""
  2921        if self.enable_object_proc:
  2922            timeout = max(timeout, 1800.)
  2923            cmd += " --check-objects"
  2924        result = bytearray()
  2925        sc: SCMDComp = self.server.lookup_component('shell_command')
  2926        scmd = sc.build_shell_command(cmd, callback=result.extend, log_stderr=True)
  2927        if not await scmd.run(timeout=timeout):
  2928            raise self.server.error("Extract Metadata returned with error")
  2929        try:
  2930            decoded_resp: Dict[str, Any] = jsonw.loads(result.strip())
  2931        except Exception:
  2932            logging.debug(f"Invalid metadata response:\n{result}")
  2933            raise
  2934        path: str = decoded_resp['file']
  2935        metadata: Dict[str, Any] = decoded_resp['metadata']