A triple bottom pattern can absolutely fail when price breaks down below the support level rather than breaking out above the neckline resistance.
False breakouts happen when price breaks above the neckline but immediately reverses back into the pattern range.
Even perfect-looking triple bottoms can fail when the broader market environment works against them.
A common practice is to put the stop-loss just below the support level of the triple bottom, essentially under the lowest of the three troughs, then wait for a clean close above the neckline before committing capital.