I am very sorry for reposting this, but adding the Solved tag might help people in the future.
I'd like to confirm how I fixed this issue, which is the same that is described in the bug report mentioned elsewhere in the thread. In /etc/smb.conf, I had the line kerberos method = secrets and keytab This didn't work because Samba didn't create the Kerberos keytab file when I joined the domain. By removing/disabling that line and restarting the machine, I fixed this issue.
