I think it’s tough to tell what’s going on. Too cold of water would definitely leave you with dough that isn’t rising much. Maybe that’s the entire problem and it’s just a coincidence that it happened at the same time as the mixer change?
Do you take the temperature of the finished dough after mixing? If so, have you seen a big difference?
We use a method that Tom Lehmann taught us. We take our ambient air temperature and flour temperature, plug those two numbers into an equation which also includes the friction factor, and it spits out what our starting water temperature should be for a given desired dough temperature.
It varies widely based on season. In the summer the water is in the 65 degree range, but in the winter it’s often over 100. In any circumstance, our dough usually comes off within half of a degree of our desired temperature (usually 85).
You may have two different things going on at once here - the change in mixer and the change in water temperature could both be wreaking havoc.
This would probably be a useful thread for you to check out:
viewtopic.php?f=6&t=3163&start=15
That will show you how to calculate your friction factor by backing it out of a batch of dough. After that, use the formula for making every batch of dough and you’ll see consistency. I didn’t do this for my first 6 years or so, but it made a huge difference in our product.
I have 3 charts in our kitchen that tell the staff what temperatures to use… One if we’re shooting for 80 degrees finished, one for 83, and one for 85. They get the ambient air and flour temperature, find where those two meet on the chart and it tells them what water temperature to use.