Blank data entry uses the data folder, and since it's on an EXT4 partition, everything is fine there.
That Grub stanza works and boots with persistent data, it's just only on iGPU. The home desktop with an RX 480 stops on the initial console.
EDIT: I'm back at the desktop and will grab the log real quick.
EDIT2: Some interesting finds.
When booting with only an AMD GPU, the kernel module is not loaded on boot. Only one monitor (the one from BIOS/firmware) is on. lsmod shows the module as not loaded.
After modprobe amdgpu all three screens come on showing the same console session. Maybe if this gets initialized sooner, the UI would load?
Here's three logs
Initial logcat before loading amdgpu manually
http://ix.io/23EV
Logcat after loading amdgpu
http://ix.io/23EW
Dmesg after loading amdgpu
http://ix.io/23EY
I will check if there's a kernel parameter I can pass to load this earlier.