Missing text and images from PDF files

I recently came across two papers that are missing images or the entire text even though the original file contains this information.I tried opening the files and resaving them and even tried various methods for compression with no luck.

This paper is missing an image
188BET靠谱吗https://s3.amazonaws.com/zotero.org/images/forums/u9824633/aioi7tzgrfmhscig4jr1.png188BET靠谱吗Import in Zotero

188BET靠谱吗https://s3.amazonaws.com/zotero.org/images/forums/u9824633/m07con8geqt19bdzfc7i.pngOriginal PDF

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This paper is missing all text.I have tried various methods of resaving.
188BET靠谱吗https://s3.amazonaws.com/zotero.org/images/forums/u9824633/1o9jkgvreyrbpt42h6dw.png188BET靠谱吗Import in Zotero

188BET靠谱吗https://s3.amazonaws.com/zotero.org/images/forums/u9824633/ahkcoai31pw6lnsepr43.pngOriginal PDF

Is there a type of PDF file which causes this?
Have others seen this?
Is there a solution?
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