Hi Fabian,

Thanks for the file.

Your image didn't show how the chain is connected, the file helps here.

The objects in your scene have a very high resolution for the mesh, which requires a lot of computing power. The Interpolation points of the Splines define the resulting mesh; lowering them might not directly lower the render quality. I made them editable (pressing the C key), to be faster (I don't have a super-fast computer).

I have used these lower-density objects to set this up, and cached the setup then.
When it was fully cached, I added the Key-Chain-Tag in its full resolution to it.
I have marked the objects used in the Simulation and the ones later added with different layer colors.

A few settings needed to be adjusted
Scene Scale, in the
Attribute Manager> Scene> Simulation> Scene> Scene Scale
and
the amount of calculations
Attribute Manager> Scene> Simulation> Simulation> Simulation> Substeps

Think of a moving object (pulled by gravity and inertia). It has a tiny search radius, which is the distance to explore if there is an object to collide with or not. If the "speed" of the objects is low, it will more often find a collision object in its search radius. If the speed is too high, the Object to collide with is too far away, and during the next calculation, already inside or even behind the Object. The Steps allow for calculating more often and recognizing a collision more often, and can react as intended.
To have these Steps always high means slower calculations, to have them too low, missing the "action".

Note: Between ring and first Chain element, there is very little space to explore a collision. Which requires a larger step number, just forced by design.

In the Rigid Tags, I typically set them to Both Sides, and the Collision shapes to Triangle.
The Auto option for the Collision shape is perhaps working for some, but not for any shape.

The Object I used for the key chain plate was reduced in the Remesher; the target here was a rough shape that would allow for a similar collision shape, but is in no way anything for rendering.

Here is your file back:
https://projectfiles.maxon.net/Cineversity_Forum_Support/2025_PROJECTS_DRS/20251104_CV4_2026_drs_25_SIkc_01.c4d.zip

Screenshot 2025-11-04 at 10.58.54 AM.jpg

Let me know if there are any questions about this process. I'm happy to look into it.

Enjoy