I didn't have this issue before installing the Beta 15.4 or 15.5 drivers (I've tried both). When I enable Crossfire, one of my two displays stops being detected. I can't see it in Windows' Control Panel or Catalyst Control Center. Disabling Crossfire makes it detectable again.
Relevant System Specs:
Windows 8.1 64 bit
Dual Crossfire 290Xs
Dual Ultrawide 1440p monitors, both over DisplayPort. Each plugged into a 290X (i.e. display 1 -> gpu 1; display 2 -> gpu 2)
I could just uninstall these drivers and go back to 14.4, but then I can't use Crossfire in GTA V as it causes stuttering.