There have been several reported issues regarding the Sophos firewall and its inability to connect to Sophos Central. This can be caused by several things. Here are some solutions to resolve this issue.
Make sure your firewall is setup properly to connect to Sophos Central.
1) Go to Central Synchronization
2) Make sure Sophos Central services is ON
3) Go to Configure and check all three boxes:
Is Your Sophos Firewall version 18.0.4?
1) Go to Administration → Admin and User Settings
2) Disable Login Disclaimer
This issue is to be resolved in version 18.0.5
1) Make sure your certificate is Sophos device and not the deprecated Cyberoam
2) Go to Certificates
3) Click the Gear option and regenerate the certificate
*This fix is specifically for Cyberoam configurations that were uploaded to the Sophos firewall