When creating a CacheManager programmatically, the JChannel supplied to JGroupsTransport must not be connected. There does not seem to be any reason for this however and it works perfectly fine to create the channel and transport, connect the channel, and then create the cache manager with the transport. And similarily with a ForkChannel the supplied (real) channel is already connected.

Here's a PR: https://github.com/infinispan/infinispan/pull/12980