On 2 occasions my smaller bedroom slide, also a Schwintek, performed just as you described. Both times it stranded me on a Sunday as I was trying to get back home. They had an electrical cable that supplied the power to the motors that had a plug connector. The connector kept coming unplugged as the slide was engaged, leaving one side of the slide without power to its motor. It took 2 trips to the dealer while under warranty to replace the power line with a longer one, and a connector that was more secure. It has worked now without problems for a couple of years, but you can guarantee I am nervous every time I operate the slide. Not sure that is your problem, but the one side motor that does not have power sounds very similar.
2015 Eagle 323 LKTS
2016 Ford F250 6.7 Diesel