It's likely one of your C4D export settings is doing this... I'm not a C4D user so I couldn't help you with specifis. When I use 3DStudioMax, there's a number of export settings that could change my geometry in undesireable ways, some of them looking a lot like what you're getting.

Your best bet may be asking someone in Cinema4D forum what are best Cinema export settings. ... or maybe one of C4D users will stumble upon this thread... (but there's no C4D in the title, so they may not...)

Looks like on export from Cinema, the mesh got triangulated, instead of being left as quads. I'm not aware of anything being able to fix that, outside of the originating application (C4D)

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