What is the biggest barriers for prior service members trying to join another branch of service?

Recruiters not getting the points for recruiting prior service.

especially if you have a break in service I would have to say lost records!!!!!

It completely depends on the people you know and what branch you are going to. As a NG member it took me maybe a month to finish the process to go active duty. but all of my higher ups were family friends and so my paperwork was fast. a friend of mine is still trying to go active from the guard and it has been over a year.