Our old Wrangler transfer case would sometimes balk at going back into gear. I learned that the key was the angle of the pavement. I would let the Jeep roll until it found a neutral incline. The dip in front of a driveway was perfect. I would let the Jeep rock back and forth until it found itself with no stress on the drive train. Then it would slip right in. Heck, even our 2012 Rubicon gets a little cranky once in a while.
You don't want to put too much pressure persuading the transfer case to go into gear. The plastic clip previously mentioned can break. Then you have to crawl underneath with a screw driver to get it in gear. You can find extensive information on jeepforum.com.
