Greets all,
A number of people have reported some issues with their super/securenode where the tracking server reports that "zend failed to return expected data".  This error can occur due to a number of reasons.

Firewall/Router config

The "zend failed to return expected data" error can be thrown because the tracking server is not able to establish a connection to the zend daemon running on your node.

If you do not have the correct port forwarded/opened, default 9033, the tracking server wont be able to validate your SSL certificate.  To resolve, please verify that the port is correctly forwarded to your instance (if using NAT for IPv4 ), the port is opened in your firewall for IPv6, or if using Google Cloud Services or AWS the port is correctly opened in the additional firewall.

Incorrect permissions applied to SSL cert private key .pem

If all you ports are open and forwarded correct and you see an output like this:

$ openssl s_client -connect

And nothing else then there may be an issue with the SSL cert being correctly loaded by the zend daemon.

To resolve, please run the following:
Modify ownership

sudo chown -R root:sudo /etc/letsencrypt/

And Modify permissions

sudo chmod -R 750 /etc/letsencrypt/

then please restart the zend daemon

Hopefully these will help resolve this issue for you, failing that, please don't hesitate to reach out to me on Discord or in the comments below.