Could not establish connection to the Collabora Online server [500 internal server error]


I have CODE installed on a VPS with Apache as proxy and NC on another host. But since yesterday I am seeing that Collabora online cannot connect to remote host, while checking further I found that /index.php/apps/richdocuments/ajax/admin.php return 500 internal server error. It’s weird because it was working as normal and suddenly this error was thrown. I have updated CODE, but still no luck.

Payload in network console:

{"status":"error","data":{"message":"Failed to connect to the remote server"}}

Restarting server/docker and reinstalling Collabora online has no effect.

Interestingly I can access loleaflet/dist/admin/admin.html, hosting/capabilities and hosting/discovery and curl -k return OK.

Here is the Apache config:

<VirtualHost *:443>

    SSLEngine on
    SSLCertificateFile /etc/letsencrypt/live/
    SSLCertificateKeyFile /etc/letsencrypt/live/

    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

    ProxyRequests 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

    ProxyPass           /hosting/capabilities retry=0
    ProxyPassReverse    /hosting/capabilities

Docker command:

docker run -t -d -p -e "" -e "username=yyy" -e "password=yyyyyyy" --restart always collabora/code

Any idea/clue will be appreciated.