The issue could have been caused by almost anything. When you use SCRIPT_DEBUG this causes WP to load all dev versions of scripts instead of the minified version. Sometimes when uploading minified JS files to the server through FTP long lines in them get truncated which corrupts the files. Doing what you did simply confirms this has happend but there isn’t a way of knowing for sure exactly what script was corrupted. The hard part is figuring out which one. When FTPing JS files you need to set your FTP client to transfer them as binary files and not text. However, sometimes this does not work because your host/server may override this and treat all .js files as text anyway. The easiest way to correct the issue is to reinstall WP and/or plugins.
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