What is the problem?
Researcher Will Dormann pointed to firewall- and DNS-related issues as the culprit. He explains that using Sequoia’s built-in firewall to block incoming connections might also block replies to DNS requests.
All the same, what I find difficult to understand is why security companies failed to adequately flag these issues during the beta testing process, or, if they did, failed to warn users that problems might emerge. It is, after all, unlikely that Apple would make any additional changes to the OS after the release of the final RC (Release Candidate) during beta testing.
With that in mind, surely developers should already have tested their solutions and identified any potential problems. That some have already updated their software to be compatible with Sequoia suggests that’s possible. If that’s true, why did other security developers fail to keep pace? (The Register claims Apple was made aware of the problems, but no fix emerged.)