L4D2 FPS stutter bug

Only happens in survivor mode, be it a map with nothing in it or a full campaign, results stay the same. No lag in infected mode. Actually count how many times the lower right FPS counter drops below 200 on both INF and SUR.

[@Serpent511]

Just a heads up. After a few more months of struggling and windows reinstalls, I found the issue. Its malwarebytes premium blocking a certain thing in Windows, best is to uninstall it and see for yourself, the lag also happens with other programs as well as the chrome plugin which adds massive cpu usage. With the add-on 25% CPU, without 0.3%.