on galaxy s6 cows, sheep, chickens, and possibly other mobs in tight space will push/glitch each other through fences when chunks are reloaded. Occasionally the mob is suffocated in the fence. Is also a problem for other block walls (cobblestone, dirt, stone, etc) but does not occur as frequently. Seems to occur because mobs are unloaded/loaded near fences and game can't determine which side of the wall they are on. Flowing water also seems to be able to push/glitch a mob through a fence/wall with the same kind of problem.