My husband makes bread every weekend, and over the last few weeks the bread has failed to rise two or three times (normally it turns out fine..this is a recent problem). Today I tried making cinnamon bread, and it also failed to rise. We thought the problem was the yeast, but my husband did a "test proof" in which he put water, yeast and sugar in a bowl and let it sit. Sure enough, it bubbled up and did everything it's supposed to do. So it appears that the problem is not the yeast. Any thoughts about what could be going wrong? The problem has occurred regardless of whether we use the bread machine or the stand mixer.