Component used: Fragment
Version used: 1.5.6

If you call Fragment.postponeEnterTransition with a delay, Fragment will post a runnable on a Handler with the specified delay as the delay. This runnable is not removed when calling startPostponedEnterTransition however which means that if the fragment is destroyed it will be retained until the runnable finally runs.

You can easily verify this with LeakCanary by having two fragments where in the first fragment you call postponeEnterTransition(1, TimeUnit.HOURS) and then you navigate to the other fragment. When leak canary runs you can see that the initial fragment is retained.

The solution should be to remove the runnable when calling startPostponedEnterTransition. This might not be feasible in the case where you call postponeEnterTransition before the fragment is attached but it feels OK to ignore that case for now.