It’s my original design, but it was rejected for being too similar.

Original artwork doesn't necessarily mean it's unique.  Everything's been done before, many times over. 

A quick search for Coffee Icons yields over 1.5 MILLION results. And that's just one search term. 

https://stock.adobe.com/search?k=coffee+icons

Other searches produce more similar assets 

https://stock.adobe.com/search?k=cookie+icons

https://stock.adobe.com/search?k=muffin+icons

Do some homework before you submit more content to Stock. 

BTW: your assets are quite nice. Try canging the title and the keywords and submit again. If they still get refused, submit them to a different stock database. 

similar is not exacly the same, it means similar. And when you check this forum: there are many posts with this topic, since Adobe introduced their new tool for moderators. Nobody knows exactly how it works and how to avoid this refusal at all.

Rejection due to similarity applies not only to the content of the asset, but also to the title and keywords.
Even if you post the same asset as an asset that has already been posted, it will not be found in searches if the title or keywords are the same.

Do a search for similar content. You are not alone. While your assets may very well be similar, it is not necessarily true. Icons, abstract designs, wallpapers, etc., are especially prone to being rejected as similar content. Welcome to Adobe Stock.