Why did my hummus go bad?
Maybe just not enough salt? Perhaps you forgot to add salt, or you switched from tahini with salt to without. Lack of salt, to most people, will make something otherwise well-seasoned taste bland.

Beyond that, since you're saying it also smells less garlicky, perhaps you used garlic that wasn't as strong as usual, or less of it.

The fact that it partially froze probably didn't matter, unless it was perhaps still partially frozen when you ate it. This is more in the domain of frozen desserts usually, but cold does numb the senses a bit, and the things you normally smell aren't as volatile at lower temperatures. We can make guesses about compromised texture and separation from freezing, but really, none of this is going to make something go from flavorful to completely bland.