Trust but verify
You're right to question the action of the slide. My slide runs off the coach battery. If the battery is not turned on, slide will not move, in or out, regardless of whether or not it is plugged into shore power. Charge or replace the battery you believe to be dead and then give it another go. "Trust but verify." A little sticking now could turn into a major jam-up later. Good luck and welcome.
"If everything seems to be going well, look around, you've obviously overlooked something."