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Could you please leave some example URL to allow us to check it?
Here is a URL to our QA site. Reply to any comment post and attach an image.
Please update the wpDiscuz Media Uploader add-on to the latest version (v. 1.3.7) and check again. The problem should be solved.
It seems you're using some optimizer/minifyer/compresser or caching plugins. Could you please disable such plugins and check it one more time?