Which Memory Latency app did you use to check your x3D L3 cache with?
Did you test the processor L3 Cache while the processor was on Idle and while the processor was being Stressed to determine if the latency is better or worse between the two states?
Found this Tom's Hardware article about the x3D Caches: https://www.tomshardware.com/reviews/amd-ryzen-9-7950x3d-cpu-review/2
If you believe your processor might have a issue open a AMD SUPPORT - Warranty ticket and explain your results to see if they believe you need to RMA your processor to be tested: https://www.amd.com/en/forms/contact-us/support.html