I just upgraded from 17.10 to 18.04. Looks good. However, mutt no longer works properly.
Specifically, within mutt, in the index view, hitting Enter no longer opens up the email message.
I verified that Enter is working on my machine in all other applications. Also, within mutt when I change mailboxes, Enter works just fine to select the other mailbox. But, for some reason, within the index view of mutt, Enter produces no response from mutt. I have not changed anything about mutt, or my muttrc. The only change in the past few days was the upgrade to Ubuntu Budgie 18.04.