I also have problems with dpm on my ASUS R9 270X. Under no load and high load
it seems stable, but with low load (e.g. playing an old game, or watching a
video with mpv -vo opengl) it is very unstable. It suddenly switches to white
screen, and the machine is hardlocked. I couldn't reach more than 2-3 days of
uptime.

Since I activated the profile method and I switch manually between low and high
states, it hasn't crashed. It also seems stable in windows.

My guess is that it can't properly handle frequent switching between power
level 0 and 1, where all clocks and voltages change at once (or maybe it's just
the memory reclocking?).