What could be the reason for having lower balance after the trade was profitable? Shouldn't the sold btc automatically show higher usdt if i made profit?

Answer

If you run multiple bots, there probably will be a dust amount of tokens left because of the minimum size for a trade is not fullfilled , this is the dust which accumulate later.

Since you trades with very small amount, you’ll notice this in percentage, but in middle amount, this usually is very small you’ll just can like collect it every weeks or months