The etcd ports reachable (tested with telnet). I hope I won't bother too much by providing a bit of info and logs, so thanks in advance... Here's what I did:
I initialized the cluster on the first node (10.9.8.21), set up kube-vip in it with a virtual ip of 10.9.8.20 and tls-san for that address.
Waited approximately 20 minutes and then tried to join the second node (10.9.8.23) which resulted in a failure. Here's the journalctl from both nodes: