Rejection due to similar content.

This is a frequent complaint lately; unfortunately, there's nothing we can to dispute the findings of the Moderators.

Did you compare your work with available content in Stock inventory? 

That's probably what it's similar to. 😉

Search Stock by your main keyword(s) BEFORE you submit.

https://stock.adobe.com/search?k="pink+rabbits"

Stock wants unique content that's unlike existing inventory.

Nothing much to be done about it. Many have slowed down or stopped submitting entirely due to this issue. Which many, myself included, believe is the workings of a poorly designed algorithm that is, at its heart, entirely random. It also begs the question, is it taking into account similar image in the database that are actually selling well (or at all), when newer images submitted might be better than those already available? This would, in a weird turn of events, suggests that Adobe Stock is placing emphasis on quantity rather than quality.