I’m in agreement with others that have posted thus far, with an additional diagnostic consideration. The purpose is to observe the actions of the gun as well as your own actions or possible bad habits (no pun intended).
Properly clean and lubricate the gun. No live ammunition in the cleaning area.
Lock the slide to the rear, remove (source of feed) the magazine, physically look and feel into the chamber ensuring that no ammo is in the chamber and that nothing is in the magazine well,
With the gun pointed in a safe direction, establish a firm grip and press the slide lock/release allowing the slide to return to battery under its own power (do not ride the slide forward). Observe that the slide has indeed returned to full battery.
With the muzzle of the now verified empty gun properly oriented in a safe direction while maintaining “a proper grip” (especially if your model has a grip safety), ensure that the thumb safety is off; press the trigger.
NOTE: If the trigger drops, the likelihood of it being the gun is next to nil. Because if the gun does not return to battery the trigger may not drop (you should have a dead trigger). Additionally, If the grip safety (if applicable) is not depressed, the trigger will not drop.
Remember the whole purpose for establishing a proper grip is to manage recoil and to mitigate muzzle flip (or muzzle rise), but also to ensure the slide returns to battery.
Now if the above is successfully accomplished, then repeat this drill during your next range visit. If all of the above goes as it should, be sure to observe what happens when you put a JHP round in the chamber, does the slide return to full battery. If it does and you experience a FTF, chances are it’s not the firearm, Notice I said, “chances are it’s not…” It could be the guide rod/spring, etc.
If nothing is wrong here, as have already been determined by the Manufacturer, that would more likely point to the type or lot of ammunition that you are using. There is a such thing as having a bad lot of ammunition. It’s rare but it does happen, more especially with handloads or remanufactured rounds.
Now, this is not an exhaustive diagnostic. But the most common FTFs occur with either limp-wristing which can cause the slide not to return to full battery, or bad or unprescribed ammunition being utilized. Also, be sure to consult your owner’s manual which may list or indicate a certain ammunition type not recommended for use.
Just trying to be of help is all…not questioning your skills.
edit: oh, and a dirty gummed up gun can cause a whole heck of a lot of nasty stuff, too. Remember what Momma said, “CLEAN IT UP!”