Happens here aswell. And the weird part is, I'm actually logged in already..
I can't be really sure on why this could've gotten worse recently, but I definitely share this annoyance.
The problem is that the SSO implementation is not ideal for applications that also support anonymous users. As a short-term solution, I will increase the session timeout to hopefully have this happen less often. As a long-term solution I'm looking with R&D on how we can improve our SSO to better support apps with anonymous access like our Forum.