@nuraydin
That because of whatever process that is used to crunch the file down corrupts them or something you need to load them into something like XnConvert and convert the .PNG to .PNG again to fix whatever gets broken in them after being crunched or whatever the hell is done to them. Once that is done then you'll be able to open the files but you'll also have to rename them as they'll have .PNG.PNG on the end of the file names.
I usually use it to convert files from WEBP to PNG to alter them and then convert them back to WEBP but also use it on the .PNG ones that people break/corrupt when crunching them.
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