We bought both at Sam's Club a few weeks ago to repackage and seal in gallon mylar bags with oxygen absorbers.
One night we repackaged 2 mylar bags of powdered milk and several bags of beans. We put oxygen absorbers from the same pack in all the bags. Everyone of the bags of beans vacuum sealed down very tight, but both bags of powdered milk never shrunk down a bit. I know it should not be a problem with the oxygen absorbers or the seal, so I'm stumped why the mylar bags full of powdered milk didn't create a vacuum like the bags of beans.
Same thing happened to me. the powder sticks to the inside of the mylar. we wiped them off waited til they dried. half took. gonna order from lds next time. rice n beans easiest to mylar seal.