Why '16 qam' & not 64qam?

Unless you need the full upstream bandwidth.  Irrespective, it should be working correctly, don't you agree ?

16 qam indicated there is a noise issues affecting that upstream  channel. 

Unless there is a loose or damaged coax cable in your system there is nothing you can do about it plus with 5 channels connected it may not make a noticeable difference to regular internet activities.