It looks like you have the setting “Hide empty staves” set to “After first system” in your layout settings. This means in the first system / first page, it is trying to show all the staves. You have 40 staves in total, so because it is trying to fit all 40 of them on the first page, it is putting them on top of each other, resulting in that mess. With the current space size / rastral size in your page setup, which configures how tall each staff is (and also controls how large notes and other symbols are), the staves are tall enough that it can’t possibly fit all the required staves on the first page.
You can do ONE OF two things:
- If you want all 40 staves to appear on the first page, in layout settings in page setup, you could decrease the current “space size” which will make the staves/clefs/notes all smaller. If you make the space size small enough to fit 40 staves per page, then all of those could fit on the first page without being on top of each other. Alternatively you could make the paper size larger in this same window. OR,
- In layout settings under vertical spacing->staff visibility, you can change “Hide empty staves” to “All systems”. Then it will hide any empty staves in the first system too, which would hide most of the staves on the first page (it will always leave at least one staff showing if all are resting, which looks like the case here).