Yeast
You might want to look into SAF "Bread Machine" or another brand's for the same purpose.
Unlike baking by hand with an oven, bread machines go by a program, hence the bread must work on the machine's schedule, and not all breads are happy about the arrangement. To be fair most machines do allow one to either adjust programs, and or at least extend or shorten certian portions of a cycle, such as rising, kneading, and baking.
Yeast in particular can be VERY fussy, and some brands/strains more than others. One can bake a loaf without any problems on Monday, and do the same again on Wednesday and have nothing but trouble.
Yeast is a living thing, and as such can be picky about the conditions it will grow and be happy under. For instance if the weather and or one's house is very humid, you may need to adjust the moisture content of the dough to compensate. Some bakers prefer not to bake at all during humid weather.