Ive noticed a lot of challenges with stacking units, how is this possible? I dont see how I can place more than one unit at an intersection on the grid
You can’t stack units in this game. Don’t break your brain trying to find a way – that functionality was removed in the first few weeks of GSB on account of being a major imbalance to gameplay. Just as you noted, units are only placeable at grid intersections.
You can still do it, sorta. But it’s been categorized as cheating ever since a patch explicitly attempt to fix it, so we more or less avoided it since then.