I have fermented my last few batches with a swamp cooler - putting my bucket into an igloo cube cooler filled with water and ice. They've all been ales. I usually start in the high 60s/lows 70s (groundwater temp) and then add frozen water bottles to drop it into the mid 60s after a few hours. Quite often it seems like adding the ice makes the airlock bubbling slow down significantly. I can't be sure that it's not slowing down because the fermentation is just naturally slowing down or if it's the drop in temp. It still bubbles, but more slowly, once or twice a minute. This has happened with several different ale strains - Safale US-05, White labs Kolsch, White labs English Ale.
So can lowering temperature too rapidly result in stuck/slowed fermentation?