Sorry for the short release cycle between 4.0.16 and 4.0.17, but there was an important feature in 4.0.17, which I wanted to release as soon as possible: JGRP-2293.
This has better support for concurrent graceful leaves of multiple members (also coordinators), which is important in cloud environments, where pods are started and stopped dynamically by Kubernetes.
Not having this enhancement would lead to members leaving gracefully, but that would sometimes not be recognized and failure detection would have to kick in to exclude those members and installing the correct views. This would slow down things, and the installing of new views would be goverened by the timeouts in the failure detection protocols (FD_ALL, FD_SOCK). On top of this, in some edge cases, MERGE3 would have to kick in and fix views, further slowing things down.
There's a unit test  which tests the various aspects of concurrent leaving, e.g. all coordinators leaving sequentially, multiple members leaving concurrently etc
I recommend installing this version as soon as possible, especially if you run in the cloud. Questions / problems etc ->