Well I know there were quite a few A300 boards initially that even had issue with Zen+ running right. Remember that was when the APUs came out to begin with. Fast forward a lot of A300 never got Zen 2 support either. Much of them because they really did have 2 key issues, bios even smaller than B350 and inferior VRMs.
So maybe this was just something that was a mistake from the get go, or they had good intentions that just didn't pan out. It would be interesting to know if any user did use that new bios that has now been pulled and it did work just fine with those APU's.
Thanks for the share!