MSI has elected to not support new processors for their existing B350 and X370 based motherboards. Found this on the TechPowerUp site today.
This is likely to get AMD calling them and asking them to update the BIOS that AMD has promised for everyone.
I have a MSI B350 board but I have an adequate CPU with my existing R5 2400G for the time being
I was more interested in a new motherboard myself with more slots for peripherals.