Are you sure about non-UBI? The toh indicates non-UBI is no longer supported, and recommends UBI if you don't plant to go back to stock. This may be the first thing to get sorted out.
Beyond the standard advice to try a reset to defaults, my only other thought would be to try snapshot. I just flashed an RT3200 to current snapshot (UBI) keeping settings and WiFi is up and working on both bands. The statistics graphs won't set up, but I know from experience I need to reset to defaults to fix that.