Please note that the SteamPipe conversation for Zombie Panic Source (ZPS) was completed and took effect yesterday. The next time you launch ZPS you will be greeted with a window prompting you to convert to a more efficient format. As of today, this update causes unwanted issues such as excessive loading times, missing textures and sounds, etc. We have notified the Dev Steam who is currently working with Steam on this issue. More information can be found on the original submitted thread by our own CPT QuaG:

SteamPipe Conversation Update Issues Thread

We will keep you posted on the progress of this.