It did eliminate the invalid hash issue, thanks. Now I have "extra files" that are non-existent. Not sure what to do with these, but I suppose I can just ignore the message until some future update takes care of it. Or is there something you recommend?
append an /apps before this (e.g. /path/to/owncloud/apps/files_antivirus) and enable showing hidden files in your terminal / filemanager. Delete the files and then run the rescan like explained in the documentation (link to that is also shown in the message in your admin backend).