I recently put a new R9 280X card in my machine, which is paired up in CrossFire with an HD 7970.
I decided to use the newer 280X as the primary card, and connected all my monitors to it (I use 3 monitors) using a DisplayPort for the main one and both DVI's for the other screens.
Every so often the DVI connected screens start reporting unsupported display modes. The display settings are correct for those screens though.
This only happened after using the R9 280X as the primary card (and of course hooking up the CrossFire bridge). I never had a single issue with the 7970 when it was on its lonesome.
Currently using Catalyst version 15.5 - this is a gaming system, so I use that for the increased performance in GTA5 and Witcher3. Version 14.12 is just terrible.
My main concern is if this is a physical problem with the card itself, or something driver related?
I can RMA it (the R9 280X), but I only want to do that if I can get some confirmation that it's a hardware issue. It's still under warranty (whereas the older 7970 is outside it's warranty now, but that still works perfectly).
I forgot to add;
The problem seems to sort itself out after about a week. Seems pretty random - if I leave it about a week, then try to turn the other monitors on again, through CCC, they work!
However, the problem will just as randomly come back again.