Great image, they don't like edited pictures @ Adobe Stock.. They want a boring, flat look...
I took a look at your image and played with it in Lightroom. I think you are showing as much information as makes sense. The gradation of the hills looks good. Where the image falls apart for me is in the handling of the foreground clouds. The black in the upper left hand corner feels like an artificial vignette even though it probably isn't. The white regions lack the beautiful definition of the lower 2/3rd of the image. I believe they are laying the exposure problem on the upper third of your image, too dark and too light with no definition. You have probably dealt with the upper third as good as can be done and might want to consider cropping it out.
You may be correct. Funny thing is, this is already a crop of the original, that to me made it a stronger composition. I have a couple others now that have been rejected on the basis of either exposure (they are also a bit baffling to me) or due to artifacts, nd one that had an intellectual property problem (logo on a building I am guessing...). In some cases I would allow for some of the artifact rejections, as they were shot under challenging light, but in other cases it is once again a bit puzzling. The major take away for me for all of this though is that they are accepting ~82% of what I submit (8 rejects out of 46 submissions) so I am just going to have to chalk it up to the way the process works and not worry too much about it, unless the percentages of rejects gets higher. I don't know of any way to fix the images and re-submit, and frankly, I like the images the way they are in any case.
Thanks for taking the time for your detailed and informative reply - much appreciated.