Your critique is based on the assumption that this is something testing could have caught. Toxins, bacterial contamination or something similar. If it is just

Your critique is based on the assumption that this is something testing could have caught. Toxins, bacterial contamination or something similar. If it is just an intolerance or allergic reaction exhibited to particular ingredients by a small fraction of the population that is very difficult to test for. Even more so if the magnitude of the reaction depends on processing of the ingredients. If they are using uncommon ingredients or process them in unusual ways it may be entirely possible that it was simply a previously unknown issue that nobody tests for, i.e. in-house testing could not have caught it either and human beta-testing could be inconclusive due to low prevalence of the intolerance. I wonder how other large food manufacturers handle such things.