Deterioration of Image Quality after Upload

[Knight Hammer]

It has come to my attention after a jpeg compression rejection that the quality of certain images deteriorates significantly after upload. This is clearly observable in the equalized version of the image. Below are the "check for dust" of the same image at the upload menu and in queue.
The compression and color clustering effects are evident in the latter image. I would like to inquire what are the possible causes of this problem and how can it be resolved. Thank you.

[Knight Hammer]

Seems the color of image #3 is a bit off in the forum. Can't tell why, but the worse compression effects between image #3 and #4 should still be notable.

[Leo 747]

Some images get converted from jpeg to webp right after being accepted in database, and that ruins the quality. It's really annoying. Quite noticeable specially in night shots and pics with blue sky, just like your example. Color banding, compression artifacts and noise stand out a lot more. Really hope this issue can be fixed someday.