It does indeed look like this was a transparency issue.
Given that it has been some time since you posted this, can I ask if you are still encountering issues with the rejection of your bundle? If so, could you please provide the associated bundle IDs?
Additionally, please take a look at the Marketplace Policy page for the most up-to-date guidelines for UGC Bundles.
Hello I finally removed the transparency for both. But I didnt manage to bring it back the robot. Because it doesnt fit without transparency. I would like to try cel shading, do you know if it’s allowed to have reverted limbs and head?