System: Ubuntu 16.04.02, using the latest 17.30 driver and a RX 470.
My display (iiyama ProLite XB2483HSU) offers the possibility of switching inputs. Typically I use HDMI for the PC running Ubuntu, and DVI for another PC.
If I switch from HDMI to DVI and then switch back to HDMI, then screen stays black and I have to go to a text console and restart lightdm.
This bug did not occur when using a R9 380 with the Catalyst driver: it is a regression of AMDGPU-Pro. Also, this bug does not happen on Windows 7 so it must be specific to the AMDGPU-Pro driver.