You're right with that. cmd fps is present in some of the b3 plugins but these are not running due to the xlrstats plugin not working in my environment yet so I don't think that will be causing it.
I see a number of references to cmd_fps in my main_shared/code directory but cannot remember where these came from.
./main_shared/code/dvars.gsx: addDvar( "cmd_fps", "int", 1, 0, 1 ); // Allow players to change cg_fovscale setting with script command ( 1-yes ; 0-no )
Does CoD4x place any gsx assets in the main_shared directory? If it doesn't I'll try to figure out where these files came from. The cod4 installation I am using was originally transferred from a Windows server and then I recompiled the server binary to make it work on CentOS 7.8 so it's highly possible I've picked up additional bits and pieces over the years it's been running.