If the walls are taller than the storey height they are placed on or are set with the base raised off the floor so extend up to the next storey they will be visible. There are a few options. You can set the walls to display cut only rather than projected, you can change the settings in the Floor Plan Cut Plane to only show the content of the current storey and you can lock the heights of the walls to the storey heights.
Lee Hankins ArchiCAD 4.5 - Archicad 26UKI Apple Silicon 5003 macOS Ventura (13.5.2)
If you set the Floor Plan Display of your walls to Home Story Only it should ignore all of your FPCP settings and only show it their home story. Unless you have multistory walls or are wanting to do plans that show current and below, doing this generally is not an issue.
You have a Curtain Wall. Its Home Story is "1. OG 1" and you are currently displaying Story "2. OG 2". This means that the Curtain Wall is not linked to the Story above as you say it, but to the Story below the currently displayed Story. If you look at the Home Story field in the Info Box, you can see it says "(Current -1)" for its Home Story, meaning the Home Story is 1 Story below the currently displayed Story.
The bottom of the Curtain Wall is 15 cm above Story 1 and it is 300 cm high. I assume your Story Height is 300 cm as well, which means that the top of the Curtain Wall is 15 cm above Story 2 which means that its top part is within the vertical range of Story 2.
It is also safe to assume that the "Show On Stories" field for the Curtain Wall is set to "All Relevant Stories". A Story is relevant for an element if the element such as a Wall or Curtain Wall is within the vertical range of the Story. Since the Curtain Wall's top is within the vertical range of Story 2, both Story 1 and Story 2 are relevant Stories for the Curtain Wall so it is displayed on both.
To make the Curtain Wall not displayed on Story 2, you can do one of two things:
1. Change the "Show On Stories" field for the Curtain Wall to "Home Story Only" so it will be displayed on Story 1 only.
2. Modify the vertical range of Story 2 so that the top of the Curtain Wall is not within it. You can do this by going into the "Document > Floor Plan Cut Plane" Dialog and changing the value of the "Show Down To" field to be higher than the top of the Curtain Wall. Since the Curtain Wall's top is 15 cm above Story 2, if you set any value greater than that (in this example I have set 20 cm or 200 mm), the Curtain Wall will not longer be in the vertical range of Story 2, so Story 2 will no longer be a relevant Story for the Curtain Wall and so the Curtain Wall will not be displayed on Story 2 (not even if its "Show On Stories" field is set to "All Relevant Stories".
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