Here's a general-purpose query you can run when there's a problem...

-- Display the blocked connection(s).

SELECT victim.Number    AS blocked_Number,
       victim.Name      AS blocked_Name,
       CONNECTION_PROPERTY ( 'isolation_level', blocked_Number )
                        AS blocked_isolation_level,
       victim.BlockedOn AS blocked_by_Number,
       culprit.Name     AS blocked_by_Name,
       CONNECTION_PROPERTY ( 'isolation_level', blocked_by_Number )
                        AS blocked_by_isolation_level,
       victim.LockRowID,
       victim.LockIndexID,
       victim.LockTable,
       victim.LockObject,
       victim.LockObjectType,
       CONNECTION_PROPERTY ( 'LastStatement', blocked_Number )
                        AS blocked_statement
  FROM sa_conn_info() AS victim
          INNER JOIN sa_conn_info() AS culprit
          ON victim.BlockedOn = culprit.Number 
 WHERE victim.BlockedOn <> 0;

blocked_Number,blocked_Name,blocked_isolation_level,
   blocked_by_Number,blocked_by_Name,blocked_by_isolation_level,
   LockRowID,LockIndexID,LockTable,LockObject,LockObjectType,
   blocked_statement

2,'SalesManager','0',
   3,'Accountant','3',
   0,,'GROUPO.Departments','GROUPO.Departments','TABLE',
   'insert into "GROUPO"."Departments" 
      ( "DepartmentID","DepartmentName","DepartmentHeadID" ) 
   values
      ( 700,''Major Account Sales'',902 ) '

The first query tells you the culprit is the "Accountant" connection, and the blocked statement is an INSERT INTO Departments being run by the "SalesManager" connection.

You can use that information to tailor the second query to show you all the candidate locks that may be responsible; change the table and blocking connection names.

This tailoring may be necessary because in a production environment, sa_locks() may return thousands of rows.

-- Display the lock(s) held by the blocking connection(s).

SELECT sa_locks.conn_name,
       sa_locks.table_name,
       sa_locks.lock_class,
       sa_locks.lock_duration,
       sa_locks.lock_type,
       IF sa_locks.row_identifier IS NULL
          THEN '[no row_identifier]' 
          ELSE STRING ( sa_locks.row_identifier ) 
       END IF AS row_identifier
  FROM sa_locks() AS sa_locks
 WHERE sa_locks.conn_name  = 'Accountant'
   AND sa_locks.table_name = 'Departments'
   AND sa_locks.lock_class <> 'Schema'
 ORDER BY sa_locks.conn_name, 
       sa_locks.lock_type, 
       sa_locks.row_identifier;

conn_name,table_name,lock_class,lock_duration,lock_type,row_identifier

'Accountant','Departments','Position','Transaction','Phantom','[no row_identifier]'
'Accountant','Departments','Row','Transaction','Read','42205184'
'Accountant','Departments','Row','Transaction','Read','42205185'
'Accountant','Departments','Row','Transaction','Read','42205186'
'Accountant','Departments','Row','Transaction','Read','42205187'
'Accountant','Departments','Row','Transaction','Read','42205188'
'Accountant','Departments','Row','Transaction','Read','42205189'

The Phantom lock must be the culprit because its the only lock with no row identifier, which matches the first query which returned zero in LockRowID.

Possible solutions are (a) add a COMMIT to the Accountant connection or (b) switch to snapshot isolation.

The Read locks are a result of Accountant running with isolation level 3... in other situations, these may cause row blocks.

You can use the magic ROWID() function to find all the rows affected by the Read locks; the second query then becomes this monstrosity :)...

-- Display the rows locked by the blocking connection(s).

SELECT sa_locks.conn_name,
       sa_locks.table_name,
       sa_locks.lock_class,
       sa_locks.lock_duration,
       sa_locks.lock_type,
       IF sa_locks.row_identifier IS NULL
          THEN '[no row_identifier]' 
          ELSE STRING ( sa_locks.row_identifier ) 
       END IF AS row_identifier,
       IF row_lock_ident.DepartmentID IS NULL
          THEN '[no row]' 
          ELSE STRING ( row_lock_ident.DepartmentID ) 
       END IF AS DepartmentID,
       IF row_lock_ident.DepartmentName IS NULL
          THEN '[no row]' 
          ELSE DepartmentName 
       END IF AS DepartmentName 
  FROM sa_locks() AS sa_locks
       LEFT OUTER JOIN 
       ( SELECT * 
           FROM sa_locks() AS row_lock,
                LATERAL ( SELECT *
                            FROM GROUPO.Departments
                           WHERE ROWID ( Departments ) 
                               = row_lock.row_identifier
                        ) AS row_ident
       ) AS row_lock_ident
       ON row_lock_ident.row_identifier = sa_locks.row_identifier 
 WHERE sa_locks.conn_name  = 'Accountant'
   AND sa_locks.table_name = 'Departments'
   AND sa_locks.lock_class <> 'Schema'
 ORDER BY sa_locks.conn_name, 
       sa_locks.lock_type, 
       sa_locks.row_identifier;

conn_name,table_name,lock_class,lock_duration,lock_type,row_identifier,DepartmentID,DepartmentName

'Accountant','Departments','Position','Transaction','Phantom','[no row_identifier]','[no row]','[no row]'
'Accountant','Departments','Row','Transaction','Read','42205184','100','R & D'
'Accountant','Departments','Row','Transaction','Read','42205185','200','Sales'
'Accountant','Departments','Row','Transaction','Read','42205186','300','Finance'
'Accountant','Departments','Row','Transaction','Read','42205187','400','Marketing'
'Accountant','Departments','Row','Transaction','Read','42205188','500','Shipping'
'Accountant','Departments','Row','Transaction','Read','42205189','600','Foreign Sales'