I want to say the b450 boards cap your ram at 2133 because you only gain 3% performance from going higher. Realistically you do not need faster ram. You can rest easy knowing your rig is still running just fine and in many cases slower ram will be more stable and less prone to random game crashes. Also it's worthy to note that some of the Intel 10th gen chips are locked to this same speed likely because Intel realized there was no real gain to higher ram speed as well
each MB has a QVL list if you want to go crazy and get hyper fast ram.
> We are happy to report that you can save some money by choosing a slower DDR4-2133 or DDR4-2666 memory, at least until DDR4-3200 or higher memory becomes more affordable. You lose practically no performance to slower memory on the Ryzen platform, when averaged across our CPU tests. The fastest memory configuration in our bench, DDR4-3200 CL14, is about 3.1 percent faster than the slowest DDR4-2133 configuration. In specific tests, the differences in performance can be larger than the average. WinRAR handles a 1.5 GB compression job 5 seconds faster on DDR4-3200 than DDR4-2133, for example.