using net ads join on a samba install without logdir (here /usr/local/samba/var)
gives the message failed to find DC instead of some other information (like no log dir ...)
/usr/local/samba/bin/net ads join -U administrator
Enter administrator's password:
Failed to join domain: failed to find DC for domain SMB4.TST
This is not a bug, "net ads join" is not a tool to verify your local installation of samba.