Why query_request 'SET' is giving error in error_messages table.

Given that the SET command syntax is accurate, try to track the command with the syntax error before.

    cat find_error.sql 
    \! rm -f suspected_queries.txt
    \o suspected_queries.txt
    select distinct(request) from dc_requests_issued
    where transaction_id in ( SELECT transaction_id  FROM error_messages WHERE message ilike '%Syntax error%' );