I think you are seeing a different issue because the other customer was getting no spam scores in MailMate (because communication with SpamSieve was blocked) whereas you are getting scores of zero (because SpamSieve happens to be classifying the empty messages as good).
Does x86 mean that you have an Intel-based Mac or that you are running an x86 version of MailMate in Rosetta on an Apple Silicon Mac?
One other customer has reported the same issue, and with a debug build I was able to see that SpamSieve is indeed receiving empty message data. So there may be a macOS bug in AppleScript or an issue with MailMate. I recommend contacting MailMate’s developer to see whether any diagnostics can be added at that end, e.g. to see which data MailMate is submitting to AppleScript. I will contact him as well.
Sorry about that. You can make a big code block by using triple backquotes.