That's probably something you should take up with Maxon support. Otherwise we will need to know a lot more. You know, those splines have settings, too, they have points and are typically used in other objects that create the actual geometry or do other things. You have not provided any of that info.
Yeah my guess would be you need to convert the bezier object to actual geometry in C4D, as until you do it's just a procedural algorhythm (whatever) that i wouldn't imagine AE could read