Hi Miguel
I haven't used 19c but I have seen those errors in the past. Things to check:
1. the database character set is correct and consistent with your Naviserver charset.
2. NLS_LANG and NLS_DATE_FORMAT environment variables are correctly set
3. in your UPDATE statement, the CLOB should be the last column listed
4. This is a bit of a wild one, but maybe you need to use TO_CLOB in the UPDATE?
hope that is of some help!
Brian