Today, I opened 10 contracts of SPX 5935/5930SP credit spread for tomorrow at a 0.40 premium and set a stop loss at a $1.00 debit. The stop loss was triggered consecutively for the 10 contracts, all at 30 minutes before market close today. However, the executions occurred at debits of 0.45, 0.50, and 0.60, respectively, and none of them hit the $1.00 debit I had set. I called Schwab, and they explained that the bid/ask spread widened at a certain point, causing the price to briefly hit the $1.00 level, which triggered my stop loss. This is really frustrating. I don't know if this is a common occurance.
Thank you.