L4D2: FPS losses or A.I lag on server?

[Shima]

I've been playing L4D2 once in a while. Without any unknown reason, it seems the game I have playing has a problem everytime I am playing on official servers or customs.
This happens today.

As you know why, when I'm playing the game, my connections are fine with fast router. The problem is, my ping is green turn yellow or red when the situations of incoming hordes.
The hordes A.I I'm playing running laggy, makes it unpredicted when or where they will attack. Worst, special infecteds will pin you down for some reason even you straight up kill it (kill a charger with melee smoothly, and then without predict you just got mauled)
I try checking my ping what just happen. My ping just completely fine on 40 ping. As the hordes comes up, the ping increasing up to 80/90 ping. Even worse, higher up to 240 ping that you don't even realize what the hell just happen.
Funny things, my fps performance still smooth with my low ping.
This happens everytime when you join random lobby games both officials and customs.

I try to find out what cause the problem by playing single player. Turns out, the hordes A.I running completely smooth without any trace of lag. No, stuck up freeze moment bs.

I try setting up, disable v-sync only. Other settings I let it high only, it still happens even when you ping only 21 and such.

Whether is the settings cause the A.I laggy, or there is a problem of an A.I performance on any server I've come across.

[Cray]

Hordes giving ping spikes is unfortunately nothing new.

I've given up trying to figure out the exact mechanic behind it, it's just one in a long line of bugs that seemingly never get fixed. For me it's only a thing on L4D1 maps, L4D2 maps all seem to work fine.

As a bonus, it often gets worse when you fire your gun, especially SMGs.

For some, it seems this problem only started relatively recently, due to either:

1) New updates to the game. Quite possible, because after the TLS update the CI on l4d1 maps were changed back to old l4d1 style CI, could be that. They also added and tweaked some animations (like the crappy looking recoil animation), could be that too.

2) New OS. Could be. Who knows.

3) New drivers. Also a very likely candidate. It's an old game and new drivers can sometimes switch to do old things in new ways, which added to the layers of abstraction with game + driver + gpu -> screen output can give any number of weird behaviours.

Wish I could be of more help, but that's all I've got atm.