Lag Issues and ?? Fog

[zza1pqx]

I have just tested a few of my maps in server.
Two of them I am struggling with.

Both of them lag, a lot.
Including the host (me) and the five players on at the time its as if your mouse is running through glue. Not flickery, but almost as if your mouse mat is not working.

All players had different setups hardware and on other maps none of us had the same problem and on the maps that were problomatic, everyone had the same problem.

Therefore its not netlag, harware or system setup issues, it must be the maps.

Thing is I work hard to keep my maps low item and one of the maps has (apart from player spawn points) only 54 items making up the entire map. I have made a lot of maps and I am confident that I know how to minimise G-Lag with good design.

The only thing the two maps have in common is light source and thick fog.
Does anyone know of any issues with using heavy fog in maps?
On one map its about 40 metres view and the other is about 60.

If not, what other reasons could it be (mapping).
Could I ask also that people answer this only if they know or have the experience to guess.

Without trying to be rude, Im not sure I want someone who doesnt make maps asking me if I have considered whether or not I have enough fans in my system........