I had something similar happen to my Seneca, also with a Power Gear slide assembly. It was my kitchen slide that was affected, but maybe yours is similar.
My system has one motor but 3 slideout "rack" assemblies. The motor is in the center and has shafts that are tied together so all racks work in sync. On my rig the collar that connected the shafts together had a 1/4" bolt, washer, and nut that tied one shaft to the next. Somehow one of the nuts fell off first and then that bolt came out out of the collar. That disconnected the front shaft from the rest. Just like you described that slideout end seemed to go the opposite direction until the slide would bind and the motor would stall.
I was able to push the slide straight from the outside to get it "unstuck", then I had my grandson operate the switch to retract the slide while I pushed that end in. It retracted and allowed me to get to the next campground. There I was able to diagnose what had happened and sourced a replacement Grade 8 bolt, washer, and nut. I used Loctite on the assembly to (hopefully) keep the nut on forever! It worked fine after that.
2014 Seneca 37TS
Toads: 2014 Ford Explorer Sport or 2013 Ford Focus ST