If you don't give it time to recompile the driver after the yum update and before a reboot, things can be in a confusing state and it won't recompile after the boot. (At least that is what I have observed).
I always run "top" after a yum update and wait till all the compilation and rpm activity disappears before I type "reboot".
If you install akmod-nvidia again, it will probably update the driver at that time and you'll be back to normal.