I got round this by having it upload files to my NAS via SFTP, rather than SMB and that works regardless.
It’s beginning of the month and I received 3 emails from my banks. While they were filed into their email folder through rules, the detach rules which @cornchip shared somehow failed to work today. I tried to trouble shoot by right clicking on but email and click Apply Rules. The mail is moved to the folder but no attachments in Finder (it’s one single rule with 3 actions: detach attachments, color mail, move to a folder). Step 2 & 3 were carried out, so I know Step 1 failed.
Does Apple Script fail often? I sometimes question why I spend so much effort troubleshooting vs just leaving it in Mails and search for them when needed. It’s one of the reasons I often gave up on Hazel and took the easy way out. Sigh.
Edit: I don’t know for sure if 15.1 have a new Mail.app which might have caused Apple Script to fail 
I read more on this later.
1 Like
To those interested, this part of AppleScript failed to work:
set theFolder to (POSIX path of (path to home folder)) & "Temp/"
Instead of using /Users/topre/Temp, it now points to Mail.app container directory, ~/Library/Containers/com.apple.mail/Data/Temp
This discussion explained that in a sandboxed environment, the home folder AppleScript command will point to the folder within the Containers.
I can’t explained why it worked in my earlier test, though, but anyway, I have corrected it.