If you're connecting to your monitor via DisplayPort try opening the AMD Radeon Settings, click on Display and make sure Scaling Mode is set to Full Panel rather than Preserve Aspect Ratio. That worked for me.
Sounds exactly like the problem I had which I solved by opening the AMD Radeon Settings, click on Display and make sure Scaling Mode is set to Full Panel rather than Preserve Aspect Ratio. Took several days of cursing to finally get it - hope this works for you.
Finally solved, thanks to an LG engineer pointing me in the right direction. In the AMD Radeon settings, under "Display", the scaling mode was set to "Preserve aspect ratio" when it should have been "Full panel".
That's all it was.
Wow.
Ok, I just blasted the card with an Xtreme burn-in with FurMark on full 3440 x 1440 res and it performed beautifully - not one black screen. Could it be an in-game issue and some bizarre coincidence with the only two games I play? The plot thickens...
Ok, thanks for the ideas. Here's where I am now. I've tried dialling down the graphics settings but that didn't work. I tried disconnecting the Thunderbolt cable and that didn't work. I tried a different mains outlet for the monitor and that didn't work...
... but what DID work was changing the...