The short version is that the RAM you buy is overclocked, so there are 20-30 different settings which can cause crashes on certain CPU/motherboard combos due to tiny, tiny variations in the silicon.

The major RAM brands you can buy don't make the RAM themselves. They just purchase, test, package and distribute the RAM.

The stats you see (6000MHz, CL40 etc.) aren't a hardware specification, but just a setting which has been tested to work reliably. Quite often, a 6400MHz RAM kit and a 5600MHz kit might be the exact same model (die) just one doesn't overclock as well as the other.

You need to run the same settings across all your RAM sticks, but when you get ones from different kits the settings which work for one stick might crash with another - Doubly so because the profile they ship with wasn't meant to be used with a different number of sticks. More RAM channels means the CPU needs to do more work, which means that the stock settings could cause instabilities and crashes.

You can't just copy someone else's settings without testing it, because even the same model CPU (say comparing one 7800X3D with another 7800X3D) the memory timings they can handle will be different. The same issue again with the motherboard.

Usually the RAM is pretty conservative with the overclock in order to make sure it works with 99% of CPUs and motherboards, but there is a reason motherboard vendors still keep QVLs(qualified vendor lists) for RAM sticks which have been tested on their boards.

If you just whack in a second stick of 16GB RAM, it might work fine. But if it doesn't, it will take a lot of time testing and tweaking settings which you might not want to, or know how to do.