When you press "sign in" on the Forum, it will take you to the Snap! login page. After signing in, it is meant to redirect you back to the forums which will automatically sign in you into them. But, instead, it just sends you to the Snap! homepage. This has been broken for a few years now.
If you don't believe me, observe the Discourse SSO redirect in the URL when you do this.
That isn't intended behavior? Oh. I just thought it was a limitation of Discourse.
When I joined in 2021, it did in fact redirect you. This behavior stopped sometime in 2022 and it's annoyed me ever since.