OK, I found out what was going on. The problem is that even though you restored your original files, the wp_postmeta table is reporting the new, resized filesizes after the bulk resize.
There is one slightly hacky way you could fix this quickly if you don’t mind your images being slightly smaller. You could go to Imsanity and change the size from (for example) 1024, to any smaller number such as 1023. Then re-run and Imsanity will find all of those images and scale them to 1023 pixels.
If you don’t want to do that and you are comfortable editing data in your wordpress database, you can optionally go to the wp_postmeta table and manually fix the records. you will see all of the attachments there. inside the column it is going to look something like this:
a:5:{s:5:"width";i:1024;s:6:"height";i:720;s:4:"file";s:20:"2014/01/Big-File.jpg" …
Since you restored your images though, those images are no longer 1024 in size – they are back to their original size (like 1600px or whatever). However WordPress isn’t aware that you put those files back.
The ideal situation is that you put those correct original dimensions in there for each image, which would be really tedious. However, if you are planning to scale them all down anyway – then you could just fake it and enter some large number (for example 1600). Just be sure that the image height/width ratio is correct. Then Imsanity will “find” them again as large images. It’s not really a huge deal to mess with those numbers temporarily.
WARNING – Before editing your database, be sure to export the data in case something gets messed up and needs to be fixed!!! As long as you backup the postmeta table and the files, though, you can always restore back to where you were.
