World is in the saves folder but is not in the single payer menu

I was trying to play on my survival world when I saw it wasn't there. So I decided that I accidentally deleted it but when it happened again to my a test world I was confused I decided to check my saves folder and both of my worlds where there! But I never got to open them ever again I don't know how this happens but I am asking you to fix this bug before it does anything very bad to any maps i'm working on.