Yes, there can be. Execution is usually certain, but price is not. In most cases, your order will be executed at a price that is close to the market price at the time the stop order is triggered. However, if a stock’s trading is halted and the stock price gaps down upon re-open (lower than the price at the time trading was halted), your execution price could be significantly lower than your sell stop price.
These situations can happen from time to time, so it's worth being aware of them.