You mention having used Brooks Cascadia and Saucony Peregrine in the past. Neither of those are zero-drop shoes, but the Altra Lone Peaks are zero drop shoes. Not sure how much you hiked in the Altras before heading out for the multi-day hike, but it takes your feet/calves time to adapt to zero drop shoes, regardless of how much cushioning they may have. Could that have been part of the problem?