FTE/extractor issues are fairly common issue, or were for a while. My 938 went back to the factory 2x and still wasn't right. I gave it away with full disclosure. I liked it when it ran right.

 
I must be the exception. My P938 Nightmare has been flawless since day 1 (day 1 being spring, 2015). No failures to extract, no slide lock/takedown pin falling out. I have shot it now in about 6 BUG matches, both IDPA and informal. Robert Burke did some work on the trigger for me. I had the right side safety removed (replaced), and use LOK grips, with a bit of purple loctite on the screws, as I do on all of my guns. The purple is easy to remove if you need to repurpose the screws for another install, but it holds very well under normal conditions.
 

I think the FTEs were our deliberate problem; we were running dirty, to try to induce failures for her to clear incase she had a problem during the test.

She passed the test, 100%.

We picked up the fixed pistol today (they replaced the frame as the grip screw threads were stripped).

Spent time in the range, ran her gun (and mine) until she was tired, and had no problems at all.

Cleaned them tonight, white lithium grease on the rails, and she's confident in the gun again. Confident enough that we bought a summer range membership (we shoot a lot at a friend's farm, but in the summer, it's a bit uncomfortable)