I am not sure why one sleep option would work and the other one would not. The only difference I might expect is the amount of time the system has to get ready for sleep.
You can replace the Shutdown option with the sleep option to see if it helps. But if the video card is involved, and from your post, it seems to be a suspect, something is not behaving. Did you remove all the Nvidia drivers prior to installing the Radeon card? You might check msinfo32.exe and msconfig.exe to see if any Nvidia drivers are still showing up.