Since its release in May, Android Lollipop has had a rough time of it. The 5.x version of Android has been one of Google's buggiest releases yet. There's one particular issue that has plagued a number of users, and continues to do so, battery drain problems.
Checking Google's Android Issue Tracker website, we see that users are still experiencing this issue, straight up to several reports even today. The problem apparently occurs on multiple different devices which have been upgraded to Lollipop, so it isn't specific to a single device.
Here at HQ, none of us have experienced this problem with any of our Lollipop equipped phones, but apparently there are hundreds of folks out there who have. It looks like the problem is not widespread enough to be a huge stain on the OS, but that is little comfort to folks who are experiencing it. It must be frustrating for Google to track down such a persnickety problem...
Source: Android Issue Tracker