That sounds like an extractor adjustment problem, although same symptom can be caused by short slide travel - like with addition of a too-thick buffer on the spring guide.
It only happens with the last round because the next rounds in the magazine help push out the empty.
One way to check extractor tension: the extractor should hold a round against the breech face. Take off the slide to check.
To add tension: short version -- remove the extractor and bend it.
There are varying ways to go about that, including using a tool designed for the job. Most of us simply clamp the back end in a vice - or stick reversed in the extractor tunnel for a quick in-the-field adjustment - then push the tip inward. A little at a time.
Check for "clocking" - the extractor rotating in the tunnel and loosing it's grip on the empty. More tension helps. Permanent fix is tighter firing pin stop fit.
Also check that the hook is intact, of course.