Reproduction

1. Create a new page
2. Edit it with the WYSIWYG editor
3. Add an image with the button  in the toolbar
   1. Select the Upload tab
   2. Browse to the image (I have used )
   3. Click Upload, Select and then Insert buttons
4. Click Save & View button
5. Go to the Attachments tab
6. Attach an image
   1. Click the Browse button at the bottom of the Attachments tab
   2. Select an image. It can be the same as the previous one but needs a different file name, or it will be considered as a new version of the previous upload.
7. Filter the Type column of attachments with Image type

Result

Only the image uploaded in the attachment tab is displayed. The one which has been uploaded in the WYSIWYG editor isn't.

Expected result

Both attached images should be displayed when filtering by image type

Notes

When exporting as a XAR, one can see that the properties mimetype and charset don't exist for the first image.

It could be the same problem as XWIKI-20159