The latest Dying Light DLC, known as Hellraid, was due to release in just a few days time on July 23rd, however, following a recent beta test, the decision has been taken to push the release back at the last minute to August 13th for PC, and August 14th for console.
The specific reason for the delay isn't clear, except to "apply suggestions" that were made following the test. Players who were involved in the beta claimed on Reddit that there were various bugs and issues, while others complained the DLC felt more like a reskin of the base game and lacking original content.
It seems more likely to address the bugs and technical problems rather than add significant new content, as the delay is only an extra few weeks. It's the latest chapter in Hellraid's troubled history. It started as a mod for Dead Island before being turned into it's own game in 2013. After several delays, Techland decided to turn the project into a DLC pack for Dying Light instead.
Dying Light: Hellraid will release on the 13th of August on PC, and the 14th of August on console.