The chart on your profile shows your total account balance in real time. It combines your cash balance and the current market value of everything you are holding. As prices move, the number moves with them.
When you sell a token, the proceeds stay in your cash balance and the chart updates to reflect the new value of your portfolio. When you withdraw to your bank or send funds out of the app, those funds leave your fomo wallet and the chart adjusts to reflect what is still there. If you made money and withdrew it, the chart drops because the profit is now in your bank. That is not a loss. That is the chart doing exactly what it should.