By default, motherboards run RAM at the “safe” setting. This is not what was marked on the box or the label on the stick.
You have to go into the BIOS’ memory section and change the profile to run at the rated speed. This is the design, I do not know the reasoning behind it, but you must always, always go into BIOS and change it to run at the rated speed or else it will be underclocked. Whether it’s an AMD or Intel CPU changes the term used for it. It’s XMP for Intel but I can’t recall the AMD name. Change it to that and save/reboot and then it will be as rated.
You can conversely choose to run it faster and mess with the timings, but I’ve never had the patience to figure out how far is far enough. I don’t even OC the CPU anymore, although I’ve had K-class since the 2700K days which would let me. Occasionally I’ll OC the GPU using the auto drivers method, but even the auto CPU OC never seemed to really make a difference I could see.