Only thing I can think of would be that you’re indexing incorrectly. Try setting the parent of your effects to only the HRP.
If it still doesn’t work, time for debugging.
local oldEffect = character.HumanoidRootPart:FindFirstChildOfClass("Trail") or character.UpperTorso.BodyBackAttachment:FindFirstChildOfClass("ParticleEmitter")
if oldEffect then print(oldEffect) else print('No effects!') end