Stairs Platform Pathfinding Still Broken

@MarSara  

I downloaded your lot and tested it.  As you built it, I got a routing fail when I tried to send my sim from the ground level to the platform landing.  I had no trouble sending a sim from the platform landing to the upper level at all but got a routing fail when I tried to send him back down to the platform.  But the reason the route failed was pretty easy to overcome.  All you need to do is increase the ground level wall height to either the middle or tall heights.  The routing fail is caused by there not being enough head room over the first set of stairs.  Another way to fix it is to lower the platform by 2 clicks. 

I set the game to winter but my test sim did not change to winter clothes just to go upstairs.  He did put on winter clothes when he got cold though so I don't think that is due to the way the house is built.  I also gave him a vacuum and he could vacuum the upper level and lower level with no problem.  When I teleported the sim to the platform and told him to vacuum, he went to the lower level to vacuum rather than on the platform.  But after either raising the lower wall height or lowering the platform, he would vacuum the platform.

So the main issues you are having are caused by the design of the house as far as I can tell.  A little adjustment or 2 of the design will let your house function properly.

Hope this helps.