[My Traded Pokemon Keep Disappearing]

So today I was Playing reborn with my friends and i couldn't beat corey so one of them said hey borrow my butterfree it will help you out

so we trade and i beat corey now when i traded with him i still had the butterfree and he also had the same butterfree and my charmeleon was gone 

and now recently my friend tried to trade me his swoobat shelly's gym and it disappeared Again 

Just Wanted to share this issue if it helps