Client can not see other clients and server

First of all, I did not know where I need to write this thread. Its a problem with render in multiplayer caused by the checkbox in world settings in level and, I think, by a bug in source code.
I want to make a tpg game with a huge world and without loading screens every some value km. My game is low poly thats why I will not to have to make a bunch of things for optimization. My landscape is huge (I dont remember, but it’s larger than 200x100 km). I imported landscape, I changed in world settings minimal z value, I puted a landscape at the middle of the map and i started. It’s working, but there is a point where my character deletes. In world setting there is checkbox like EnableCheckStillInWorld and disabling it will make a map unlimited. But there is a point where physics works very bad. I made a landscape 10 times smaller(character too) and there is no bugs with physics. I worked a lot an d than I decided to start with multi-player, i puted some player starts, played with 2 players (listen server) and after a few seconds server character deletes from clent screen, but in server screen all good. When I start dedicated server I have a same problem - few seconds and all one client van not see other client. After some time i figured out that when my player starts are in the middle of the map (0x,0y,0z) there are no bugs. I think engine replicates world variable for all server’s characters (copies in server) and only for client’s own character (controllable character in client screen) but not for other copies of characters. Is there a way to do not have this bug?

It s not EnableCheckStillInWorld, its EnableWorldBoundsCheck, sorry.