Sensu Go Backend gets stuck "initializing store"

I have setup an etcd cluster (using 3.3.18) with 3 nodes using TLS encrypted communication. Testing with etcdctl on all 3 nodes works fine, cluster health is good.

Next I set up an sensu-backend cluster (using CentOS 7-RPMs for version 5.15.0-7782) and configured TLs accordingly.
The first start of the sensu-backend nodes was single, thus I deleted /var/lib/sensu/sensu-backend/etcd before starting the cluster configuration.

Now sensu-backend starts up on all 3 nodes without error, the last line being logged is
Dec 1 15:43:36 area3-sensubackend3 sensu-backend: {“component”:“backend”,“level”:“debug”,“msg”:“Initializing store…”,“time”:“2019-12-01T15:43:36+01:00”}
sensu-backend then is stuck - no errors, no ports opened up (thus no querying with sensuctl), and it does not shutdown on request, it has to be killed hard.

On the etcd cluster side of things nothing is logged either.

Communication between the two is verified using openssl s_client.

I do not know where to start troubleshooting - please advise.