Thanks for the review and glad to hear it has helped you over the years. Do you have any suggestions on why the regeneration should and could be faster?
I have not checked how it works but it seems that the regeneration needs to keep the web page open, which may indicate the process is updated from the client browser or something. If that’s the case, it could be run straight in CLI mode entirely from the server.
Also, on one website, I’m running into the same issue as https://wordpress.org/support/topic/image-regeneration-stops-at-9/, though it stops at 13%. I don’t think the server is to blame since it’s a WordPress multisite install and all the other sites work, but maybe there is a picture in the collection that Image Magick doesn’t like at all. I have seen no log, though.