Like any firearm, the function of the M&P®380 Shield™ EZ™ Manual Thumb Safety pistol can be influenced by the type and quality of ammunition used with the pistol. In the case of the M&P 380 Shield EZ Manual Thumb Safety, we have found that in very rare circumstances, ammunition that produces a high level of felt recoil can cause the manual safety to move from the fire to the “safety on” position during firing. Should this occur, you will not be able to fire the next round unless and until the manual safety is reset to the fire position.
At Smith & Wesson, we are committed to designing and producing firearms that meet the highest quality and performance standards. To ensure that every Smith & Wesson handgun meets our standards for reliability and performance, as of April 4, 2018, we have engineered the manual safety so that it will be less susceptible to the influence of ammunition weight, velocity and loads. Any M&P 380 Shield EZ Manual Thumb Safety pistol produced before April 4, is eligible for a no-cost upgrade. To determine if this consumer advisory applies to your pistol, please utilize our serial number verification tool.
https://www.smith-wesson.com/mp-380-shield-ez-consumer-advisory