Inconsistent overnight proofing
I'm making pretzels. Every evening I prepare the dough, put it in the fridge, and the next day (~16 hrs later) I take it out, let it rest, and then bake it.
The problem is, what I'm taking out of the fridge in the morning is *very* inconsistent (rise differences of nearly 100%). The amounts and ingredients I'm using are always the same (measured by weight, ~70% hydration), the mixing procedure is always the same (water into mixing bowl, add yeast, let it sit for a minute, add sugar, mix for a few seconds, and then add the flour/salt mix), and so is the fridge (consumer-grade).
I tried different brands of yeast, tried increasing the amount of it, but it's still a gamble of what I will find in the morning.
Could it be the fridge (i.e. whether it goes through the thaw cycle at just the right moment), the mixing procedure, or where should I start troubleshooting?