Nexus hub keeps getting misaligned
It sounds as if you adjusted the barrel adjuster out too far, the last time you adjusted it, and damaged the threads on the adjuster.  When the shop cleans and lubes it, it is fine for a few days, and then gets stuck again, because the threads are cross threaded or stripped.  If the damage is relatively minor, it can act normal until it is under a little higher tension than average, and then "jump" out of place, whereupon it will be stuck, and out of adjustment almost immediately.

Of course, not having it in front of me, this is just conjecture.  You should find a shop you are confident in and explain the multiple issues, and ask them to find the problem.