I'm not sure whether you are saying there was a change in behavior with the same file or whether you mean that files from the same source had a change in behavior. I suspect that it is the latter and would be surprised if it was the former. I have no expertise in programming of files. But what I can tell you is that every time a jpeg file is opened and saved, it may be changed, even if no edits have been made. Not all programs that can save the file will save it in exactly the same way. Similarly, if you upload or download a file to or from social media like Facebook for example, the file may be changed. The changes may also depend on the device or browser that is being used to upload or download the file. As I understand it, the non-compatible jpeg files that we are discussing here have a very small piece of code that does not comply with the standard, yet makes the file unreadable by Elements and other programs that conform to the standard.
However, having said all of that, you raise an interesting issue and I will request that Adobe consider increasing the compatibility of the files that it can handle. There may be a perfectly good reason why Adobe will not open these files and will not allow them to be used in Elements without first making them coform to the jpeg standard. That is beyond my pay grade to answer.
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