When I created the archive of Smartfeed 3.0.6, apparently some files that exist in folders were copied into the root folder. It didn’t hurt anything but it’s incorrect. I have republished the archive on this site. You might want to delete these files and reinstall it in /ext/phpbbservices/smartfeed.
Aside from this error there were no code changes.
It was always correct if you downloaded it from the GitHub Smartfeed page.