Could I see a screenshot of the inspector for the STM components? Basically, there's a couple settings in STM that are there for legacy purposes, so it's possible for STM to follow a layout wrong or differently if not configured right.
For the contentsizefitters, make sure they're set to "preferred size"... even though the verticallayoutgroup has a notice that pops up, iirc, it seems to be the right way to do this kind of thing if I'm understanding correctly...?