Bread-Bakers v096.n025.3

It doesn't sound to me that the humidity is a problem.  As a 
professional baker, we proof bread in as much as 90% humidity.  I'm 
wondering if you have a heat problem with your machine.  If the yeast 
gets overly hot during the rising process, it will die and not rise.

Is there a fan or heat mechanism that is malfunctioning?

The only other thing I can think of is that your bread is getting 
underkneaded.  Without proper kneading, the bread does not have the 
strength to stand.

Good luck - Susan