The SDO_GEOM.VALIDATE_GEOMETRY_WITH_CONTEXT function fails for 3D Compound line strings geometries as discussed over here. This is illustrated by the following sample:

2d:

with t1 as
(
select 1 id, SDO_GEOMETRY( 2002,NULL,NULL, 
         SDO_ELEM_INFO_ARRAY(1,4,2, 1,2,1, 3,2,2), 
         SDO_ORDINATE_ARRAY (       10,10, 10,14,6,10,14,10)) geom 
from dual
)
select 	id
      , CASE g.geom.st_isvalid()
          when 1 then 'valid'
          when 0 then 'invalid'
        END validness
      ,	sdo_geom.validate_geometry_with_context( theGeometry => g.geom, tolerance => 0.001) reason 
from t1 g;

produces:

ID VALIDNESS REASON
1  valid     TRUE

While the same geometry in 3d is considered invalid:

with t1 as
(
select 1 id, SDO_GEOMETRY( 3002,NULL,NULL, 
         SDO_ELEM_INFO_ARRAY(1,4,2, 1,2,1,   4,2,2), 
         SDO_ORDINATE_ARRAY(        10,10,0, 10,14,0,  6,10,0,  14,10,0)) geom 
from dual 
)
select 	id
      , CASE g.geom.st_isvalid()
        when 1 then 'valid'
        when 0 then 'invalid'
        END validness
     , sdo_geom.validate_geometry_with_context( theGeometry => g.geom, tolerance => 0.001) reason 
from t1 g;

ID VALIDNESS REASON
1  invalid   54530 Point:0,Edge:1,

A Quick workaround for this is to convert the geometry to 2d:

with t1 as
(
select 1 id, SDO_GEOMETRY( 3002,NULL,NULL, 
         SDO_ELEM_INFO_ARRAY(1,4,2, 1,2,1,   4,2,2), 
         SDO_ORDINATE_ARRAY(        10,10,0, 10,14,0,  6,10,0,  14,10,0)) geom 
from dual 
)
select 	id
      , CASE SDO_CS.MAKE_2D( geom).st_isvalid()
        when 1 then 'valid'
        when 0 then 'invalid'
        END validness
    ,	sdo_geom.validate_geometry_with_context( theGeometry => SDO_CS.MAKE_2D( g.geom), tolerance => 0.001) reason 
from t1 g;

result:

ID VALIDNESS REASON
1  valid     TRUE

hope this helps, Stephan