Not all R-1100s are not created equally. Generally, with R-1100s (but, I'm not sure about the LT-20) the longer the barrel the smaller the gas vent area. Remington has tried to second guess your application and size the gas vent area accordingly. So, if you have a long barrel with a full choke, they assume you'll be using heavier loads. On the other hand, if your R-1100 has a short Skeet choked barrel, they assume you'll be using lower pressure loads. Also, the longer the barrel, the greater pressure: So, a "goose" barrel will have a smaller vent area than a short target barrel. Consequently the longer barreled R-1100s have a slight tendency for more gas vent fouling than the shorter ones.
If you've exhausted all options and your R-1100 still doesn't cycle, then you might consider having a qualified smith increase the vent area. This is an alteration not to be done without fully understanding the consequences.