Furniture disappears when trying to access the upstairs

springcoffee I'm not sure but this might be related to your use of the platform on top of the foundation for the porch. 

So, my 1st suggestion is to change the wall height to medium to see if that will fix it.  It looks like you are using the short walls.  So, it might be a clearance issue with the porch causing it because it looks like the top of the sliding door may be too high to use on a short wall due to the platform and the positioning of the awning to clear the top of the door.  If that fixes it, then you'll have to reconfigure how you've done the porch or leave the walls at the higher height.  Another way to check for that is to move the platform, everything on it and the awning above away from the rest of the house at least 1 tile and see if it still happens after lowering the door to the default position.  I'd also try moving just the awning first as that might also be causing the problem since it appears to be higher than normal.  If either way does fix the problem, then paint the ceiling or if you find there is no ceiling, build one, then paint.  Same with the roof.  Then try putting the platform and everything else back where it was to see if the problem returns.  If it does, then you'll know what the problem is.

My 2nd suggestion is to change the foundation you have extending out from the wall 1 tile and under the platform.  As it is, it looks like the platform is floating.  Once you get the foundation even with the building wall, use 2 platforms at different heights to get the same look but not have the larger one look like it's floating.  I also suggest that you leave the platform next to the sliding door only one click high rather than the two clicks high that it appears to be.  

My 3rd suggestion is to try building the lot along the grid.  Right now, it's diagonal.  Building diagonally does seem to create a lot of problems at times, depending on what a builder has done.  Some things just don't seem to work very well for diagonal builds that work fine for the same build built along the grid lines.  I know that basically means a complete teardown and rebuild as there is not a way to simply rotate the entire structure by 45 degrees.  I've done it before when I rebuilt the Oasis Springs Gym lot, and it wasn't easy.  I only mention doing that as it could possibly be the cause of your problem.

If none of those things work and if you are willing, I am willing to troubleshoot the lot to see if I can find a fix for what you have going on.  All you need to do is upload the lot to the Gallery and reply here with the name of the lot and your userid if different than the one you've used here (springcoffee).  I will download it and see if I can find the problem and a fix for you.

Hope this helps.