Lots of good advice so far, so do all the stuff recommended here, but 1 FTE in the first 500 rounds does not necessarily indicate a real, on-going problem.
Top three causes for FTE in my experience, when weapon is clean:
- Operator error. For FTEs, that almost always means limp wrist.
- Mechanical: Extractor/Ejector.
- Ammo.
If it was clean in the first place, you've checked the springs, extractor, ejector, etc., and you didn't limp wrist it, you probably had an ammo issue. Small chance at a magazine issue.
When shooting a new auto loading pistol, I usually try to induce failure by limp wristing it on purpose, to see how sensitive it is to that issue. For the outside possibility of a magazine issue, if it happens again, make note of the magazine you were using, and which place in the mag the FTE round was. Mag problems usually show up in feeding, not ejecting, but a goofy follower or feed lips dragging
can affect ejection. Again, very small chance of this being the issue.
Problems are easier to solve if they repeat, and I would not happily trust my life to an auto loader I had less than 2000 rounds through. Shoot it more. A lot more. Preferably with lots of different magazines, and lots of different ammo. If it only happens with one particular load, it's smarter IMO to just avoid that load than tinker with the gun. Multiple shooters can be helpful, too. Helps eliminate operator error as a cause.