Hi [mention:d640b0f4007841e8944a8afe66e9541d:e9ed411860ed4f2ba0265705b8793d05],
The KB article has been archived as the issue has been resolved since November 2021.
If you still experience issues with the security heartbeat certificate, I would suggest you post on the Sophos Firewall discussion board or raise a support case.
Hope that helps,
R