With crypto this is very common due to slippage and liquidity. A bot can’t account for slippage or liquidity. And a big issue with crypto is that many times during huge market volatility, the exchanges might go offline.
In a backtest you never account for this issues hence the bots are never going to be reliable.
You are correct talking about the volatility and the challenge it cause to the exchange. The volatility time is a moment of uncontrollable market movement that will force the platforms to go off maybe temporarily and this time, the bots can't also function. The volatility is also a time that traders have accused exchanges of manipulation and whether true or false is to be determined.