On newer Linux distributions, there’s a hard regression either within the kernel but more likely some cross-kernel/user-space interaction issue leaving newer Linux distributions unbootable.
While Ubuntu 18.04 LTS and older Linux distributions boot Zen 2, to date I have not been able to successfully boot the likes of Ubuntu 19.04, Manjaro Linux, and Fedora Workstation 31. On all newer Linux distributions I’ve tried on two different systems built around the Ryzen 7 3700X and Ryzen 9 3900X, each time early in the boot process as soon as trying to start systemd services, all systemd services fail to start.
I’ve confirmed with AMD they do have an open issue surrounding “5.0.9” (the stock kernel of Ubuntu 19.04) but as of writing hadn’t shed any light into the issue. AMD has said their testing has been mostly focused on Ubuntu 18.04 given its LTS status. I’ve also confirmed the same behavior with some other Windows reviewers who occasionally dabble with Linux.
So unfortunately not being able to boot newer Linux distributions is a huge pain. I’ve spent days trying different BIOS versions/options, different kernel command line parameters, and other options to no avail. On some Linux distributions after roughly 20~30 minutes of waiting after all systemd services fail to start, sometimes there will be a kernel panic but that hadn’t occurred on all systems at least not within that time-frame.