You packed on Tuesday and the lid shut. You repacked on Friday with the same clothes and had to kneel on it. Nothing was added. What changed was the sequence.
A case is packed to the height of its worst decision
Hard cases have a fixed internal depth, and every item is competing for the same vertical budget. Put a bulky, springy item in early and lay flat things on top of it, and the flat things inherit its height — the lid now closes on the tallest point rather than on the average. Packed in the other order, the flat items go in first as a dense base and the bulky item compresses down onto them. Same clothes, same case, two or three inches of difference. This is also why repacking mid-trip so often goes worse than the first attempt: you rebuild in the order things come to hand, which is almost never the order that stacks.
Fix the order by fixing the container
The reliable way to stop making the decision at all is to stop packing loose. Once each category lives in a cube, the cubes are the only things you stack — four flat-sided rectangles of known height instead of fifteen garments of unknown loft. You pack the case once, in an order you can repeat, and mid-trip repacking becomes putting four blocks back rather than rebuilding a jigsaw. Shoes and anything with a hard profile go at the hinge end where the depth is greatest, wash bag last so it is on top when you land, and the flat things go underneath everything as the base.
If the lid fights you, try emptying it and reloading flat-to-bulky before you conclude the case is too small.