There is a limit of 25 elements per level on the content tree.

This is not a problem for the content tree in content structure and media library, as you may always select the parent element and the navigate the results in main panel, but it is really a BIG problem in the content tree when you want to select a related content item (while editing related object fields).

You have no way to see objects that are in the 26th or later position and therefore you cannot select them. Only workaround is currently to create more folders and avoid to have more than 25 elements in them.

But it should be possible to navigate the full list of child elements when viewing the content tree while editing a related object field.

Using the search panel is also not a solution as it does not work as expected. Will create another ticket for it.