Source of Soft 404 errors?

Hi,
Our Google Webmaster tools Search Console says that we are getting loads of “Soft 404” errors. It lists URLs that I can’t decipher at all. I can’t figure out where
google is finding these URLs in our site, or what might be generating them.

Based on the URL details, I suspect that they may be coming from the AddToAny plugin.

Hoping that someone can point me in the right direction. The URLs shown in the Google Search Console look like this (for example):

http://www.councilofindustry.org/wp-admin/admin-ajax.php?action=PopupBox&current_view=0&fb_id=1&theme_id=1&open_with_fullscreen=0&open_with_autoplay=0&image_width=800&image_height=600&image_effect=fade&enable_image_filmstrip=0&image_filmstrip_height=70&enable_comments=1&enable_likes=1&enable_shares=1&enable_author=1&enable_name=1&enable_place_name=1&enable_message_desc=1&enable_image_ctrl_btn=1&enable_image_fullscreen=1&enable_object_info=0&slideshow_interval=5&enable_image_facebook=0&enable_image_twitter=0&enable_image_google=0&current_url=name%3D3d-printing-goes-hollywood&image_id=137&image_id=

And following that URL simply gives a page with the error message “The image has been deleted.” No 404 error message or anything like that.

I’m guessing that this PARTICULAR error was generated on the blog post here:
http://www.councilofindustry.org/3d-printing-goes-hollywood/

And guessing(?) that perhaps(!?) it comes from the AddToAny sharing plugin, which does pop up a modal window…

Why are we seeing these errors?
Why is Google indexing these URLs?
How can I correct those?
If I can’t correct them, what can I do to have those directed to a proper 404 error page?

ANY suggestions that might lead me in the right direction would be helpful!

Thanks!

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