Do you have the old vs new picture? I think I have the new C ring but that was in November 2022. Is there another revision after that?
Here you are, old on the left, updated on the right. Height 10.6mm vs. 11.0mm, on the second picture you can see the new version with less cutout, improving the tilting of the old version.
As mentioned in many posts: this is not only the compression ring, the separate stem and its top cap have an issue, as well, there were issues with compression plugs but also tolerances of Velobuild frames come into play (IMO).
In the end the customer has to solve for one or more of these issues...painful but good luck!