It happens rarely, but the barrel of the safety may have broken.

A really good detail strip of the slide and a cleaning might reveal broken parts. Spring changes might be in order, but if you're not experienced with the 3rd generation guns and/or mechanically handy, you might want to hand this off to someone who is.

Before you do that, field strip the gun and function check the various frame levers. If you press the ejector down flush with the frame top, the trigger should disconnect from the hammer. If the hammer is cocked and the decocking lever is depressed, the hammer should drop. When the trigger is pulled, the safety plunger lever should move upward.

Now with the slide assembly upside down, safety off and the barrel removed, depress the safety plunger and hold it in the down position. With a pin punch, push the firing pin forward. It should stick out of the breech face about 1/16 of an inch and retract when you release the firing pin.