Of course, such big new releases are not without faults and no company is safe from launching a dud. As you probably remember, iOS 8.0 caused a lot of headaches for users and Apple alike (especially the 8.0.1 update), so did iOS 8.1, which was released as soon as the new iPad Airs were announced. This prompted for updates to be released in rapid succession, with some ironing still left to be done.
Well, Google's Android is also angering early adopters, as the hot-out-of-the-oven 5.0.1 update has been reported to have a nasty memory leak, which tends to take up 1.3+ GB of RAM, resulting in on-screen apps constantly being force closed and the used phone auto-returning to home screen often. A thread on the Android Issue Tracker forum has been opened and users have reported various Nexus devices to be afflicted (2013 tablets, Nexus 4, 5, and 6), so it appears no one is safe.
The good news is that the cause of the memory leak may have been pinpointed and the thread has been closed and marked as “FutureRelease”, which means that the fix will be added to an incoming update (which update, and when, is unknown, but we'd imagine – as soon as Android devs can arrange for it to happen).
source: AOSP Issue Tracker via Phandroid