Game switches profiles on same account

So this is very confusing. My sister owns a survival world and I play on it everyday. But sometimes when I play I'm on a separate profile with items that are from when I played split screen, now keep in mind I never went on a different account only 1. But sometimes when I play I have my good items from current not from when I played split screen. I don't play on split screen anymore but ever since I did I've had 2 separate profiles which are random when I join. If you would like any clarification just ask, especially if any of this is confusing