We recently began rollout of version 22.214.171.124 of the Sophos Web Appliance software. Your appliance should receive this update over the coming week if it has not already upgraded.
This release addresses an issue that was caused by the recent expiry of one of the root Certficiation Authority certificates used by Let's Encrypt - "DST Root CA X3". This would cause certificate validation to fail for certain poorly-configured web servers.
For release notes, please check the following link:
The link you mentioned here does not work.
I've edited the post with an active https link.
Thanks for pointing this out.