Maybe you missed the problem. Maybe you missed the problem. English is not my main languages so I will try to explain again.
I will try to describe in detail what can happen
When new topic is made a mail goes out to all users.
They click on that link to topic
https://urlsite.se/topic/001
If user not alreade logged in they redirects to login form.
If they login is right everything working good.
But if not they made a new try. And here the problem starts.
I understand that they dont can redirects to that topic and thats fine, no problem.
But the problem is they can not access that topic anyway.
So if they first visit https://urlsite.se/topic/001
They can not visit that topic at all. Every click redirects them to login page again.
All other topics is working.