I cant understand why is index used with item 00123 and not with 00938, same SQL

Hi,
anybody have an idea why index is not used with item 00938, but 00123 do? I have already rebuild the index, but no change.

SQL:
SELECT LAGORT.ARTNR AS C1, LAGORT.LAGERORTNR AS C2, LAGORT.LAGERPLATZ AS C3, LAGORT.MENGE AS C4, LAGORT.LAGERORTNR AS C5, LAGORT.ISAVAILABLEQTY AS C6
FROM LAGORT
WHERE LAGORT.ARTNR = '00123';


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Ausführungsplan
----------------------------------------------------------
Plan hash value: 635348658

-------------------------------------------------------------------------------------------
| Id  | Operation                   | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |             |    57 |  1482 |    33   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| LAGORT      |    57 |  1482 |    33   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IX_LAGORT01 |    57 |       |     1   (0)| 00:00:01 |
-------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("LAGORT"."ARTNR"='00123')