I have a similar problem while joining games, but has a larger scope than any of you.
In fact while I'm trying to solve that problem (reinstalling roblox by manual uninstalling and deletion of roblox files), I still get a problem.
I diagnosed the problem as "DNS server isn't responding"
Also read the thread on page 10. This is where my previous posts that contains the details of my problem goes:
https://forum.roblox.com/Forum/ShowPost.aspx?PostID=60176919
Former S&Ier