It looks like most vendors don’t have their boot menus updated to support the new ECC memory they now support…

[…]Once you have an ECC-enabled memory controller, a motherboard with the right traces, and a few sticks of ECC memory, the next step is whether the BIOS/UEFI properly supports ECC. This is where things start getting a little bit iffy. AMD placed all the responsibility for ECC support on the motherboard manufacturers, and they aren’t really willing to step up to the plate and assume that responsibility…you will find out why in the conclusion. As a result, while most motherboard manufacturers have now come to acknowledge that their motherboards are indeed ECC enabled, that is the extent of their involvement. Not one is offering an enable/disable option in the UEFI, and we haven’t seen anyone but ASRock and ASUS have any ECC settings available at the moment.

This lack of settings severely hampers the overall ECC functionality, since a big part of it is that the motherboard should be able to log errors. Right now, no such logging capability exists. Thankfully, there is a possible software solution. The operating system – if it fully supports this new AM4 platform – should have the ability to log errors and corrections. If it does not, the hardware might be silently correcting single-bit errors and even detecting ‘catastrophic’ two-bit errors, but you will never know about it since there will be no log. That’s what we are going to look into next.

To conclude this page, we strongly suspect that just about every AM4 motherboard likely has ECC enabled, or at the very least will in the future. Most motherboard manufacturers certainly aren’t actively supporting it, or even unlocking any of the features that accompany it, but they don’t appear to be maliciously disabling it either. At this point in time, they simply have other way more important things on their plate, like improving memory support, overclocking, ensuring that IOMMU is functional, etc. Furthermore, we strongly suspect that they are presently unable to unlock all of the necessary settings without a newer CPU microcode from AMD.

http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/75030-ecc-memory-amds-ryzen-deep-dive-2.html