About the black screens - The GPU might have problem with low vertical blanking values, that's why it black screen and have "input signal lost". Closing the game should do the trick, the problem is, alt+f4 not always work, and sometimes even closing won't work, because the monitor can't reset from it's state.
Black screen crashes/ crashes , stutter - there's GPU-RAM or RAM-VRAM pipeline/cooperation problem.
Downclocking -either power management, or bad driver cooperation with game engine[like UE4 for example].
AMD probably knows about that, but it doesn't hurt to inform them, maybe they haven't come up with these ideas, so it might give them a lead.
The fact that they haven't fixed the issues still can have two explanation:
-they don't know what's causing the issues
-they know what's causing the issues, but have no idea how to fix it
If it's the second case -all hope is lost. RDNA-GCN hybrid support will be ditched, and we will be left with junk. They will flesh out RDNA 2 probably, so the only solution will be either buy RDNA2 GPU or go NVIDIA.