I see profit but my Bitcoin (BTC) balance goes down - how come?

Trading bot counts only deals profit, it doesn't count profit/loss caused by the price change of your coins. I.e. you have Bitcoin on your account, bot brought you 10 USDT profit, but BTC dropped in price to USDT and you have lost 11 USD just by having BTC on your account. So you have lost $1 at this point.

Another reason can be the Bitcoin price increase.

Example:

Why my Bitcoin balance goes down