If the problem occurs it will be with the Starlight edition and probably also the Founders edition. To get the case transparent the material is lighter built. Also the PCB is transparent and more fragile built. - And as such the Basic beige version should be the most solid built version.

Not every example is the same. Some buyers have no complains about it. Even realize only there indeed some flex when they read about it. - Some do have complains.

It is quite possible that some unites where not put together exactly like they should have been. Parts not exactly aligned. What can could explain the difference in experience.

As the C64U is very simple to open and there are very few parts one should be able to fix the issue by realigning the offending parts.

There also have been made 3D printed braces to re-enforce the internal structure.