Samba's password lockout tests are timing dependent, but not all of them need the same strictness in regards to time. 4d0fd1a421ad4a3ca19ed954ee91fcc36413b017 is a backport to 4.9 of this fix in 4.10, but it should be backported again to 4.8 to make this area flap less also.
The bug is only for a 4.8 backport, which we WONTFIX if we haven't already.