I believe your assumption is right. It sounds like Amazon needs to see evidence of a visible CE certification mark, which confirms the safety of the product. I know you sent them an image in one of your images but the next agent at Seller Central probably missed it and didn’t read the earlier messages. I would recommend that you consolidate all your images onto one PDF with arrows that clearly show and illustrate where each of the items they need to see, are located (sometimes we need to overcommunicate 😉
I have created an example below. If you add this PDF every time you respond to a ticket for this issue, it means ever SC agent will see the important information.
Then ask them, what additional information do they need to approve your entry into the category: