I just got the game yesterday on PS4, and I'm not sure if I've encountered a bug or if I just don't understand something about power armor. After I got my first power amor, I went back to the workshop at the Red Rocket and left my power armor there. It is no longer there, and I cannot find it anywhere I took it. I only have one piece of the armor left, and I've stored that in the mod station. Does anyone know if this is a bug, or does power armor just go to some specific location when you're not using it?
If you left the fusion core in the power armor, there's a good chance than an NPC just got into it and decided to either: A) Steal it; B) Take it for a joy ride.
Enemy NPC's like Raiders can apparently steal it if you leave it like that, or friendly NPC's can take it while they patrol a settlement.
So if you want to leave your Power Armor without the fear of having someone steal it, take the fusion core out and take it with you.