I've only had that happen once, the solenoid came from the factory with a torn inner rubber seal, the solenoid piston bore got rusty. The solenoid comes off of the started hard. I needed a certain size thin walled socket to get mine apart and if I remember correctly an impact driver and even then it was rough.
Never seen it on a Bosch, Mitsubishi or Chrysler Jeep starter. But on other brands the contacts in the solenoid would burn a little and could momentarily weld
They didn't weld solid but would hang closed. The starter relay is always a possibility. Or even the ignition switch.
I've packed my Bendix full of mud, it usually failed to engage though and didn't hang fully engaged. The solenoid spring is fairly stiff and strong.
Had one starter with a broken shift fork.
I'd clean up the Bendix, coat it with oil, put the nut on the solenoid lead and bench test it (just the Bendix movement) maybe twenty times. You can hear if it hangs or fails to engage completely. The end bushing can get pretty sloppy, but I've never really seen that cause any issues, but it's possible the side play in the shaft could jam something.
GOJeep has a good write up on starter cleaning and service, if you want to take it apart for a closer look and maybe some lubrication. Keep any lube away from the brushes and use any lube sparingly, it may migrate and if the brushes get coated in oil or grease the starter doesn't work well.
