Ever since the 1.11 update came out, lingering potions would start functioning differently in some of my worlds, while in others they are completely unaffected. Lingering Potions would entirely stop giving potion effects to all entities including the player, and the particles would appear to linger on forever, and can possibly cause permanent lag. The only way to get rid of this is to enable cheats and type in "/kill @e", which kills everything including the particle cloud.