REGEXP_INSTR on a CLOB database column raises ORA-03113 end-of-file on communication channel

Oracle database 19c, same error in Toad and SQL Developer

This error message is raised only for table rows that have CLOB column with text exceeding 4000 characters. When the SQL query is filtered to only select records with CLOB column less than 4000 characters no error message is raised.

Oracle documentation confirms that REGEXP_INSTR works for CLOB but does not state that it is limited to only 4000 characters and the error message causing session abortion is cumbersome.

Please advise how to get REGEXP functions to handle CLOB table columns exceeding 4000 characters.

Thanks.