pylxd: Debugging pylxd.exceptions.ClientConnectionFailed?

I’m trying to connect to an LXD cluster using the steps from this guide but I get a pylxd.exceptions.ClientConnectionFailed error:

>>> from pylxd import Client
>>> client = Client(endpoint='http://192.168.123.121:8443', cert=('lxd.crt', 'lxd.key'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/pylxd/client.py", line 290, in __init__
    raise exceptions.ClientConnectionFailed()
pylxd.exceptions.ClientConnectionFailed

The hosts are on the same subnet (.120 is my host, .121 is the LXD cluster member), ping works, port 8443 is open, the cert files are in place, I can get an answer back with wget:

host_120:~$ ping -q -c 5 192.168.123.121
PING 192.168.123.121 (192.168.123.121) 56(84) bytes of data.

--- 192.168.123.121 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4081ms
rtt min/avg/max/mdev = 0.435/0.691/0.881/0.179 ms

host_121:~$ netstat -an | egrep "8443.*LISTEN"
tcp        0      0 192.168.123.121:8443    0.0.0.0:*               LISTEN     

host_120:~$ ls lxd.*
lxd.crt  lxd.csr  lxd.key

host_120:~$ wget http://192.168.123.121:8443/1.0
--2018-07-08 06:10:27--  http://192.168.123.121:8443/
Connecting to 192.168.123.121:8443... connected.
HTTP request sent, awaiting response... 200 No headers, assuming HTTP/0.9
Length: unspecified
Saving to: '1.0'

1.0                                 [ <=>                                                                        ]       7  --.-KB/s    in 0s      

2018-07-08 06:10:27 (339 KB/s) - '1.0' saved [7]

The saved file contains “1503 0100 0202 0a” in hex. I did a capture too: pylxd.pcap.zip

Versions:

• OS: Ubuntu 18.04 (Bionic) server
• Python: 2.7.15rc1,
• pylxd: 2.2.7
• LXD: 3.0.1

Is it something with pylxd or the LXD cluster? Is there a way I could get a detailed error message, not just the exception?