Dunno how to describe it really, wasn't lag so much but the map was virtually unplayable.

A little description goes a long way. I know it's a small and difficult map, but what is "buggy" about it?

It was like lag, stop start as you move around, very annoying, buggy.

Play was not smooth, as it should be. It was only like this on this map, other maps were fine so it's not the server or me, it's that map.

maybe it had something to do with FPS?

It was probably a combination of the rain effect and the many emitters. Setting your world detail to low and turning off weather effects would fix that. But, I was considering taking it off anyway, because of its size, so now it's gone.