According to the IL-2 Sturmovik website, AMD Crossfire has been “temporarily disabled”. One poster saw that was stated that way all the way back in 2013 and asked when it was going to quit being “temporary”.
Enabling Crossfire and setting it to AFR Friendly or Compatible the game will scale great but will have lots of flashing. This screen flashing seems to be a real pain with almost every game one time or another. I sure wish there was ways of modding profiles like nVidia Inspector does for nvidia.