Missing rows in Visual DBA, exist when queried specifically
(Please forgive the SQL Server test case - the problem is common to all SQL implementations because that of common semantics mandated by the SQL Standard.)

Even though you have used a LEFT OUTER JOIN, the semantics of SQL can convert this to an implied INNER JOIN if you improperly put constant-test conditions in a WHERE clause instead of the JOIN clause. The example below ilustrates this.

Preliminaries to create test data:

if object_id('Address') is not null drop table Address;
if object_id('Person') is not null drop table Person;
create table Person (
    ID          int identity    not null primary key clustered,
    Name        varchar(10)     not null unique nonclustered
);

create table Address (
    ID          int identity    not null primary key clustered,
    PersonID    int             not null references Person(ID),
    SequenceNo  int             not null,
    Address     varchar(40)     not null

    ,constraint NK unique nonclustered (PersonID,SequenceNo)
);

insert Person(Name) values
     ('Fred')
    ,('George')
    ,('Ron')
    ,('Ginny')
;

with data as(
    select * from(values
            ('Ron',   1,'Attic bedroom, The Burrows')
           ,('Ron',   2,'Junior Boys Dorm, Gryffindor House')
           ,('Fred',  1,'Blue bedroom, The Burrows')
           ,('Fred',  2,'Senior Boys Dorm, Gryffindor House')
           ,('George',1,'Green bedroom, The Burrows')
           ,('George',2,'Senior Boys Dorm, Gryffindor House')
           ,('Ginny', 1,'Pink bedroom, The Burrows')
    )data(PersonName,SequenceNo,Address)
)
insert Address(PersonID,SequenceNo,Address)
select 
    Person.ID,
    SequenceNo,
    Address
from data join Person on data.PersonName = Person.Name
;


Now these two queries

select *
from Person
left join Address on Address.PersonID = Person.ID
               where SequenceNo       = 2
;
select *
from Person
left join Address on Address.PersonID = Person.ID
                 and SequenceNo       = 2
;


respectively return

ID          Name       ID          PersonID    SequenceNo  Address
----------- ---------- ----------- ----------- ----------- ----------------------------------------
3           Ron        2           3           2           Junior Boys Dorm, Gryffindor House
1           Fred       4           1           2           Senior Boys Dorm, Gryffindor House
2           George     6           2           2           Senior Boys Dorm, Gryffindor House

ID          Name       ID          PersonID    SequenceNo  Address
----------- ---------- ----------- ----------- ----------- ----------------------------------------
1           Fred       4           1           2           Senior Boys Dorm, Gryffindor House
2           George     6           2           2           Senior Boys Dorm, Gryffindor House
3           Ron        2           3           2           Junior Boys Dorm, Gryffindor House
4           Ginny      NULL        NULL        NULL        NULL


Note how, despite the LEFT OUTER JOIN which one expects to ensure that all Person rows are returned, the placement of the condition SequenceNo = 2 in the WHERE clause instead of the JOIN clause coerces the join into an INNER JOIN; so that Ginny is dropped from the first result set.

This is a specific example of how, more generally, the occurrence of a NULL value in a field being tested violates intuition. One loses the Excluded Middle, so that when a predicate A may be NULL it is no longer tautologically true that A or NOT A will give you all rows; all rows with a NULL value for A will be silently dropped.