The problem is with the size of the open world.

Faced a problem - the size of the open world is limited to a square of 20km by 20km. If the character, or transport, tries to cross the border, it disappears.
This size doesn’t suit me since the planned size is 50km by 50km.
Maybe someone knows how to remove the restriction and increase the game world?

Check the World Settings panel. What you are interested in is the checkbox Enable World Composition (check) and Enable Worlds Bounds check (uncheck) and Enable World Origin Rebasin (check). Read up on those thing in more detail on the documenation site.

Thank you very much for the answer.