Chunks don't update in servers made with server.jar

When I log into a server made by minecraft_server.1.9.4 jar I connect successfully and sometimes no chunks spawn; other times chunks spawn and then they don't update. a moment later the connection will time out.

This maybe a problem with minecraft_server.1.9.4.jar It also happened with 1.9.3 and I think it happened with 1.9.2 and 1.9