Seems like the “story” is still developing on the github issues thread. My intuition says that it’s possible that some of the people on there are operating on incorrect premises or have an incomplete understanding of how rdrand works. Not that I know anything about the latter either, just find it hard to believe that AMD would mess up something like that again(?).
Why? RDRAND is known to be broken on almost all AMD platforms in one way or the other, and has had ample issues even on Intel. I have a very hard time believing that any competently built cryptographic library would actually rely on it.
Even systemd could get away with just using it to seed a software RNG given what they use it for (generating UUIDs before the kernels random number generator is available), and anything running after boot is probably better served by using /dev/(u)random.
That code appears to work perfectly on my 5950X on an ASUS x570 board. It is either particular CPU chips, the 5900X model, or a fault in that Gigabyte BIOS.
I remember with the 3000 CPUs the RDRAND bug was fixed in the BIOS updates. Perhaps Gigabyte forgot to include that one in their latest.