When examining page errors, I'm finding this one, which leads to a file that I'm guessing doesn't exist in the newer version of the ckeditor library:

Not Found

The requested URL "/sites/all/libraries/ckeditor/plugins/fastimage/lang/en.js" was not found on this server.

And also this error where the fastimage plugin folder is present, but now the only two subfolders/files within it are: dialogs/fastimage.js, images/noimage.png:

SyntaxError: Parse error

$: HTMLDivElement
__proto__: Object

There is also this separate error where the file is present but there is a parse error:

SyntaxError: Parse error