I have ran into an all familiar problemb.
high end video card users aren't experiencing the problemb but a lot of us who have cards that are just sufficient are experiencing framerate drops and this is causing the server to skip over some information because the client side computer can't handle all the information it is getting.
I'm running 500Mb Ram and a 128Mb Radeon 9200 video card and I can definately tell the difference when you propigate too many actors in a scene for a system such as mine to display.
here's a short set of screen shots of where I monitored the FPS and how it is effected by the amount of static meshes in a scene with collision enabled.
As you can see......when I look towards the infield I have a dramatic drop in framerates........compound this with all the rocket trails and other projectiles plus the vehicles and you have all the makings of a map that will overload the lower rated video cards or systems with too much rendering information and not enough time to render it all and keep up.
my solution is to eliminate the line of trucks as 24 individual static meshes and make it into 2 separate static meshes....plus 2 invisible static colision meshes
I need to optimize the material of the invisible collidable meshes to one material so that it takes less available memory to detect the mesh collisions.
I need to lower the vehicle weapon fire rate to take some load off the processor.....tracking hundreds of projectiles with trail emitters takes up a lot of memory.
Lots to fix.....but I am learning a lot about how the unreal engine handles active scenes.......it all can be made to work well if set up properly.........I just need to learn how to do it properly