light loads in 9mm sig sauer p228

You didn't mention your load, but I'd suggest boosting it 10-15% and see where that puts you. Light loads don't work the action hard enough for proper function, as you found out. The gun still fires but there isn't enough energy to shove the slide fully rearward, and thus you get a FTE, failure to extract/eject.

Increasing bullet weight will also add more impetus to the slide's movement.

As PJ said, you need to increase your charge OR your bullet weight a bit.

The third option is to install a decreased weight (reduced power) recoil spring. Be careful with this one since if you shoot full power (defensive) loads with a reduced recoil spring you can start damaging the handgun. Keep track of which spring you're using if go you this method.
http://www.gunsprings.com/Semi-Auto%20Pistols/SIG-SAUER%20(SIGARMS)/P-225,%20P-228,%20P-229/cID1/mID4/dID253