A fix is available for this below:
To use this beta, just deactivate/delete your existing Patreon WordPress plugin. Then upload and activate the zip you downloaded from dropbox above. When the fix is out in the new version, you can just upgrade to the new version from your WP admin.
What this fix does is to use image’s own contents to uniquely identify the image instead of using its filename from Patreon.
This will cause all images to be re-imported once when you start a full import (manual or auto), but after that images wont come in duplicates. And correct images will be inserted in all posts, this time from singular image sources. (If an image is in two posts, only one image will be used properly instead of 2 images.)
If you have not used the images which the plugin imported before in any post, then you can delete them manually. You will have to do it just once. Sorry for the discomfort.
If you encounter any issues, just let me know.