Communication programming is a fertile field for ambushing bugs, because many things in communication are random and/or are not under programmer control:

Many programmers sooner or later encounter problems with stable production applications that worked fine for months or years. By that time the original developers forgot all details. Or they do not work with the company anymore.

The problems range from subtle to catastrophic. For example, an application may suddenly crash, or refuses to start, or stops accepting user requests.