I had this problem in the previous J2.54, and after upgrading to latest J and Gantry (2.5.5 & 3.2.19) it still persists. The sidebars (a,b,c) are not presented on the side but underneath the content. It does not seem to matter which layout pattern I try in my mainbody or how I assign the modules for side display. Some of the pages will display, but the home and others will not. For example, the "Feed" module shown now (on the left)should be in sidebar-a.