I tend to over-explain things to the point of confusion, so I've uploaded a video showing the problems in action, and a screenshot so you can see how I'm handling the collision for Platform behaviours. I'm assuming the way I'm doing it sucks, and there's a much better way.
This only happens on slopes. I have flat platforms that don't give me any issues whatsoever, but these slopes are a nightmare. Sometimes the players starts falling through the platforms half-way along (I've tried moving platform boxes in multiple different set-ups, with no luck). The edge of the slopes always turns into a flat surface for some reason, despite the boxes clearly being sloped. And when using the down and jump keys to fall through a platform, the player gets caught up inside the platforms, meaning you have to press down and jump a few times before you drop all the way through.
I'm trying to get this working for branches in trees. One of the branches on the left is especially problematic. I've even tried copy/pasting the platform boxes from a branch that they're working on to the problem branch, and the player still falls through. I've spent two days trying to solve this now.
Video is on Youtube over here.
Screenshot to show collision boxes (with platform behaviour. Branches are tiled backgrounds without any attributes checked).
Any help and advice would be awesome! Thanks for reading