Unable to establish SSL connection

I’m trying to debug my Collabora server to confirm if it’s running OK. However, I’m seeing the following:

$ wget -O - https://office.mydomain.com/hosting/discovery > /dev/null 
--2019-01-15 22:40:29--  https://office.mydomain.com/hosting/discovery
Resolving office.mydomain.com (office.mydomain.com)...
Connecting to office.mydomain.com (office.mydomain.com)||:443... connected.
HTTP request sent, awaiting response... 502 Proxy Error
2019-01-15 22:40:31 ERROR 502: Proxy Error.

So proxy error. Now I’m looking at the virtual host file, I can see where it’s trying to reverse proxy to:

<VirtualHost *:443>
ServerName office.mydomain.com:443

# SSL configuration, you may want to take the easy route instead and use Lets Encrypt!
SSLEngine on
SSLCertificateFile /etc/letsencrypt/live/office.mydomain.com/fullchain.pem
SSLCertificateChainFile /etc/letsencrypt/live/office.mydomain.com/chain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/office.mydomain.com/privkey.pem

SSLProtocol             all -SSLv2 -SSLv3
SSLHonorCipherOrder     on

# Encoded slashes need to be allowed
AllowEncodedSlashes NoDecode

# Container uses a unique non-signed certificate
SSLProxyEngine On
SSLProxyVerify None
SSLProxyCheckPeerCN Off
SSLProxyCheckPeerName Off

# keep the host
ProxyPreserveHost On

# static html, js, images, etc. served from loolwsd
# loleaflet is the client part of LibreOffice Online
ProxyPass           /loleaflet retry=0
ProxyPassReverse    /loleaflet

# WOPI discovery URL
ProxyPass           /hosting/discovery retry=0
ProxyPassReverse    /hosting/discovery

# Main websocket
ProxyPassMatch "/lool/(.*)/ws$" wss://$1/ws nocanon

# Admin Console websocket
ProxyPass   /lool/adminws wss://

# Download as, Fullscreen presentation and Image upload operations
ProxyPass           /lool
ProxyPassReverse    /lool

So (SSH into that server to run locally) I’m trying to send a request to the reverse proxy destination, cutting out the proxy:

$ wget -O - > /dev/null 
--2019-01-15 22:20:25--
Connecting to connected.
Unable to establish SSL connection.

So there is a problem with my SSL connection? The keys do exist and I’ve used Let’s encrypt for this and other sites that work fine over HTTPS.

More info if it helps:

$ sudo netstat -lnpt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0*               LISTEN      21147/docker-proxy
tcp6       0      0 :::80                   :::*                    LISTEN      7489/apache2    

$ sudo docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                      NAMES
c714e3b8883d        collabora/code      "/bin/sh -c 'bash st…"   24 hours ago        Up 2 minutes>9980/tcp   vibrant_haibt

Is there anything I might have done wrong in my virtual host setup? Anything else I ought to be checking? UFW, etc?