I'm having a very similar issue with an instance of Discourse I maintain. Multiple users report being intermittently & randomly. signed out after upgrading to Safari 16.4. Occasionally, requests to my site from Safari 16.4 fail to send a user's session token cookie, despite it being present in Safari's storage. This results in my server seeing that missing cookie and "correcting" the mistake by signing the user out. This does not happen on every request, but it's always the same cookie that gets "dropped." The main difference b/t our cases is that my cookie is not a session cookie, it has an expire time of 365 days.