That’s very weird, you were in the group when I wrote the post
I am thinking there was something wrong with your click on the link and you didn’t get put in the “Site Security Group” of the same name as the Forum Group. The syncing of the two is the time delay.
I put you in the Forum group, and it disappeared, I did it again and it disappeared again. So you must not be set in the site’s security group.
I will now go and put you in both.