Dave Platt wrote, among other things,
"In either case, if you screw an N male connector with a bad center pin
into an N female, the male's pin can force the split segments of the
center female pin outwards. Once this happens, a _good_ N male
connector's pin may not make reliable contact with the female's
damaged center pin. Intermittent nastiness can occur."

I've seen people suggest that you can mate an N plug with a BNC jack in
a pinch, but what you describe is _exactly_ why you should never do
that. The N plug center pin is a distinctly larger diameter than a BNC
center pin.

Also note that there exist 75-ohm N connectors. Do not try to mate
them with 50 ohm versions. A 75 ohm plug in a 50 ohm jack is likely to
not make good contact, and a 50 ohm plug in a 75 ohm jack may cause
damage to the jack.