Twinkal,
It's difficult to say what's going on without knowing the URL or markup that is affected, but the most likely explanation is that your requests.get() call is hanging due to a change in whatever service is being accessed, and the problem is happening before any Beautiful Soup code runs.
Since the code works for five other URLs, and stopped working on a particular date with no changes to your code, I would look at the URL that's causing the code to hang. For example, see what is happening when you open that URL in a web browser.
On the other hand, if you've found an HTML page that makes Beautiful Soup+lxml hang during parsing or searching, I would very much like to see that HTML page.
Leonard