Probably going to have to open the slide, get a flashlight and peek under the slide behind the rubber seal.
Possibly the slide rides on some channels and is moved on a rack, similar to rank and pinion steering.
Maybe it's skipped a tooth or 2 and is out of sync????
please report back with your results
Life's A Long Song
2008 Fleetwood Terra 33L, SCT, Safety-Plus, Trac Bar, Koni, Banks Stinger, Sumos, '16 Canyon Duramax Toad