Why is Safari logging me out of all websites when switching tab groups?

I'm running Ventura 13.4.1 and for about the last week, preceding installing the latest update, I have been experiencing an annoying issue whereby I am logged out of all my page (Google, Facebook, Messenger, AWS etc) when switching between Tab Groups in Safari. It doesn't happen immediately on switching, so I'm not sure if it's the switch itself that triggers it, or if it's some time-based issue, but it's immensely frustrating. This last time, I was logged in to my social media in my "Personal" Tab Group, switched to my "Work" Tab Group, where I stayed for no more than four or five minutes. When I switched back to Personal, I had been signed out of all websites.

I have cross-site tracking prevention turned off.

Has anyone else noticed this and can hopefully suggest a solution?

Thanks!