Thank you everybody for your replies.
This PTR-9KT is going back to PTR for a warranty service.
FTEs in this type of firearm are usually caused by a faulty extractor spring or the extractor itself. The parts are cheap and easy to replace. So I gave it a fair try. Then I clearly identified, the problem is related to a defective part. Now is the time for PTR to do the right thing. From all I saw on line, PTR has really great customer service, so I don't anticipate any problems.