That sounds alarmingly like a problem that unfortunately does not fall under warranty coverage (owing to its being more than 12 months since purchase.)
Erratic errors are neither settings nor immediate environmental conditions, nor 'hard damage' like breakage from being dropped, nor storage conditions such as the memory card being full or write-protected (and you say the images were stored, even if they were all black.)
Given that the problem started under conditions of dubious 'exposure' or light intensity levels, it might be not so much a picture processing/compression circuitry path problem, as a problem with the automatic light sensor, perhaps.
So in sum, I have considered what you have described so thoroughly, and I have to conclude that something is wrong... perhaps processing circuitry, perhaps light sensor (or circuitry associated with it), but still: the camera will need servicing to work well again.
Given that it is out of warranty (only just! unfortunately) you would have to pay for such repair-servicing as the camera apparently needs.
The page to go to, in order to initiate an Olympus USA repair-servicing of your camera, is here:
under the heading toward the lower left titled, REPAIR YOUR PRODUCT.
I'm sorry that a better conclusion is not possible under the circumstances, and good luck with the repair of your camera (or its replacement, should you so choose and prefer.)
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