Working on a heavy project using World Partition with UE5.3.2 I encountered some problems with landscapes. Firstly, some were not packaged, you could see them in the editor, in standalone, but not packaged. Then it was worse, they not only disappeared if they were not eliminated directly. Now, the solution is simple: Verify the integrity of Unreal Engine, that will solve this type of problem.
I hope this helps someone.