SQL & PL/SQL :: Oracle External File And UTF-8 Query

Encountering an issue with an Oracle external table. We get the following error when we load a particular file in this table:

ORA-12801: error signaled in parallel query server P000
ORA-29913: error in executing ODCIEXTTABLEFETCH callout
ORA-30653: reject limit reached
ORA-06512: at "SYS.ORACLE_LOADER", line 52

We have narrowed this down to a text field in the file that contains the following text (text obfuscated):

XXXXXXXX ł XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

This is nominally 40 characters long, which matches the maximum field size, but it is being rejected because it appears the 'ł' character is causing Oracle to interpret the length as 41 characters instead. If I remove a X then the file loads without issue.

We tried this in a new schema we created where we added the same table and used the same file. There was no problem at all. The oracle database has the following settings:

NLS_CHARACTERSETUTF8
NLS_NCHAR_CHARACTERSETUTF8
NLS_LENGTH_SEMANTICSBYTE
NLS_LANGUAGEAMERICAN

The table is defined as follows:

CREATE TABLE XXXXXXXXXXXXXXXXXXXXXX.XXXXXXXXX_INTERFACE
(
XXXXXXXXXXXXXXXXXXXX VARCHAR2(40 CHAR),
XXXXXXXXXX VARCHAR2(40 CHAR),
XXXXXXXXXXXXXXXXX VARCHAR2(40 CHAR),
XXXXXXXXXXXXX VARCHAR2(40 CHAR),
[code]........

We tried adding the following attributes but they did not seem to make any difference:

CHARACTERSET UTF8
STRING SIZES ARE IN CHARACTERS