I'm sure it is not the case. There is NEVER a guarantee on a stop but you state "next day" above. That is not a stop market. A stop market is to execute immediately when a trigger is hit. Brokers have obligations not to move the market. If the stock's last trade was $19 and bids disappear to $5 bid, TD would have some serious explaining to do if they allowed the market to move down 73% on one small trade. Read their terms. I'd be willing to bet they do not say guarantee and include something to the tune of "best efforts".
In regards to the OP's question. We are sitting here speculating on large gaps and other extreme situations when we have not seen details of the placement of the order, the trigger, the stock, the time, etc. IB's last metrics show 1.76 million DARTs per day in October. They must have thousands of stops per day and the OP seems to be a rarity stating his stop order wasn't honored. I thus think it is reasonable to jump to the conclusion this is operator error. I could be wrong but without knowing the exact details on how the order was submitted we may never know.
when i place a stop market order. I put the duration "good till canceled." For TD ameritrade, the default is 90 days. So my stop market sell order will execute no matter what for the next 90 days when the price either hit the market price or below.