I've just upgraded to 2015.4 and I'm setting up a new 20 page report document from scratch.
I need to set up several master pages and when I go edit the master and go to Layout > Margins and Columns, click the up/down arrows on the gutter width doesn't change. I can change, column number, margins, enable layout Layout Adjustment, but Gutter does nothing. Lock Column Guides is unticked.
As a temporary compromise, I've placed text boxes with columns on the masters, but I've used this feature for 10 years and it's really frustrating when core features get broken with updates.