DBConnection Error(DBConnection.ConnectionError) tcp recv: closed (PGPool)

The next thing I would try would be to look at the logs on the pgpool side of things and see why it is closing the Postgrex connections. If that doesn’t work spin up Wireshark and look at the TCP stream and see who is sending the FIN packet (it’s most probably pgpool), if you know that pgpool is closing the connection you’ll have to figure out why it is doing that