.1 duplicate files in either assets, private asset, uploaded images, uploaded files, or templates caused by esync.
The short term fix to correcting the .1 duplicate file issue is to delete the .1 and delete the respective knowledge files.
If you do not know how to find or delete the knowledge files then please read this knowledge base article on that.
The long term solution is to update the windows service to 9.0 or higher. You do not have to update the site if you do not want to. If you want to know how to do this please refer to this knowledge base article.