According to this article, AMD is working on a fix for an FMA3 issue that is locking up Ryzen powered PCs. Here's the lowdown:
Thankfully for Ryzen chip owners, AMD knows what the problem is but isn't giving out much in the way of details. According to Digital Trends, the fix requires changes to the BIOS on motherboards. AMD is working on those changes, which will then be distributed to motherboard manufacturers who will then issue a patch. For anyone experiencing these Ryzen system hangs, it's a case of patiently waiting and checking your motherboard's support page for the required BIOS update.