I’m glad to hear that my work has proved useful to you.
I have a possible solution that may help with your subdomain issue. I see you have registered a lot of domains to this plug. If you have multiple domains on the same server then I could modify your registration on gotmls.net to allow you to scan one level higher in your directory hierarchy. This could make it easier to scan the parent of a sublevel domain or siblings of your primary domain under the parent directory. Let me know if you want to try this, and what domain would you use as your primary registration.
I don’t think this will help specifically with your 404 error though. I have not seen this happen before. If you are willing I would like to take a closer look at your site and debug this issue for you. Then I could release an update that may help others who are having the same problem. Is there any way I could get a temporary admin account on that site so that I can run the scan myself and see where it’s breaking?
Thanks for the offer to donate (I would be very appreciative). I am willing to help you through this in good faith and then, when we are done, you can decide how much it is worth to you and donate appropriately.