WinHTTrack comes also with the commandline version of it.
Perhaps you are more successful with your download job when using the command
line approach.

Have a look/get inspiration at examples to increase the speed like here:

<https://techienotes.blog/2016/07/28/the-fastest-way-to-download-a-website-offline/>

<https://archiveteam.org/index.php?title=HTTrack_options>