According to Digital Trends  AMD is not explaining what has been causing the screen freezes - it has said that BIOS changes will be distributed to motherboard manufacturers to resolve the issue.

“We are aware of select instances where FMA code can result in a system hang, We have identified the root cause.”

AMD released three Ryzen-branded desktop processors at the beginning of March that plug into motherboards based on AMD’s new AM4 socket. These include the Ryzen 7 1800X, the Ryzen 7 1700X, and the Ryzen 7 1700. All three reportedly cause a hard system lock when running certain FMA3 workloads.

For those who came in late, FMA is that the processor can compute A+BxC in one step before rounding the final result. The “unfused” method involves BxC first, rounding the number, adding that to A, and rounding the result.

Ryzen’s issue with FMA3 was that basic user privileges could crash it, Even more, code using FMA3 could be executed on virtual machines running on AMD’s upcoming Zen-based “Naples” processors for the enterprise.