When I was racing Downhill, many riders would "dial out" the largest cog (and sometimes the smallest, turning a 9-speed cluster into an 8 or 7-speed) by cranking in the limiting screw to avoid the very thing that happened to you. If you look at how close the rear derailleur is to the spokes, you may see just how easily a good bounce, some flex in the spokes, etc could cause the cage to get caught, especially with long cage SGS derailleurs. This can also happen to a derailleur with worn out pivots. If everything checks out OK, take a closer look at your limiter spacing. The derailleur should be set to go no further than the jockey pulleys lining up with the inside face of the largest cog.