source3 messaging_init() calls server_id_db_init() (where names.tdb is created) with lock_path. source4 imessaging_init() otoh wrongly used the special lock_path subdirectory "msg.lock":
    
> find /opt/samba/ -name names.tdb
/opt/samba/var/lock/msg.lock/names.tdb
/opt/samba/var/lock/names.tdb

> tdbdump /opt/samba/var/lock/names.tdb
{
key(14) = "notify-daemon\00"
data(27) = "28609/12756565486113779780\00"
}

> tdbdump /opt/samba/var/lock/msg.lock/names.tdb
{
key(15) = "winbind_server\00"
data(8) = "28593/0\00"
}
    
With a follow up patch both source3 and source4 messaging now use the same names.tdb which is what we want:
    
> find /opt/samba/ -name names.tdb
/opt/samba/var/lock/names.tdb
    
> tdbdump /opt/samba/var/lock/names.tdb
{
key(15) = "winbind_server\00"
data(8) = "26434/0\00"
}
{
key(14) = "notify-daemon\00"
data(26) = "26452/3454520012124001687\00"
}