I found this problem about a month ago, but then forgot about it. Now I tracked it well. I am searching by keyword, with New sorting. I am searching for my own pictures, because I know the dates of approval.
On page 3 I see image 2114674** approved on August, 18.
On page 4 I see image 2121668** approved on August, 22. How did it get there? It must be on first page! It's only about 9 hours after approval. And it's 500000 times younger. How can my new images sells better, when they're under older ones?
On page 12 I see image 2114833** approved on August, 18. Why not, right?

 Another keyword, another pictures. I just picked up random images and their page numbers. They're not only mine now.
 Page 1 - 2122187**
 Page 2 - 2121170**
 Page 7 - 2118580**
 Somewhere here must be my image 2118098** (August, 20). But it's not. It was here, when I thumbed through catalogue for the fist time. But now it's gone.
 Page 9 - 2117566**
 Page 14 - 2114454**
 On page 20 I see my image 2121668** and almost all my batch approved on August, 22. A also see it on page 22 . Where it must be? On 2 or 1, I think.

 Conclusion: New images can be messed up and mixed in sorting for a few days, until they loose their freshness.

 Similar experience, anyone?

PS: Post was written on SS forum two days ago. I checked searches from above again - images are in the same order, just gone deeper.

Easy to say with small portfolio and part-time contribution
I feel unexpected sales drop, as lots of us discuss here and there, too. And now I have no chance to compensate it. But instead, I know "33 things I can do and still see my works dive into the abyss"

Actually, we had long periods when everything was fine. Or problems were so quiet, that nobody mentioned it. So I prefer to think about this, as a default state. Yes, we have a Big Bug at least once a year for a couple of months. But if we do not report it, then who will? If we don't care about our money, who will? It's all about money, because I could post my illustrations in blog instead

True, very selective and I only upload one photo from any shoot. I don't want to confuse buyers. (yes really, one best shot of a subject most of the time) Exception is a racing event when I might do two or three of a driver, in different settings.

Interesting. I don't do this and upload more than one photo from a shoot, not 50 similar pics either, but definitely more than one. Nevertheless, I usually have a favourite, one photo that I think will sell better than the rest. More often than not, buyers do not agree with me...