The only guess I have is that perhaps the size of the subquery is considered a CLOB?  I have no null values for the fields selected AFAIK.

    SELECT DISTINCT 
        kbq_ent.qid AS kbq_ent_qid,
        kbq_ent.category AS kbq_ent_category,
        kbq_ent.consequence AS kbq_ent_consequence,
        kbq_ent.diagnosis AS kbq_ent_diagnosis,
        kbq_ent.last_service_modify_datetime AS kbq_ent_last_servic_1,
        kbq_ent.patchable AS kbq_ent_patchable,
        kbq_ent.pci_flag AS kbq_ent_pci_flag,
        kbq_ent.published_datetime AS kbq_ent_published_d_2,
        kbq_ent.severity_level AS kbq_ent_severity_le_3,
        kbq_ent.solution AS kbq_ent_solution,
        kbq_ent.title AS kbq_ent_title,
        kbq_ent.vuln_type AS kbq_ent_vuln_type,
        kbq_ent.discovery_remote AS kbq_ent_discovery_r_4,
        kbq_ent.cvss_base AS kbq_ent_cvss_base,
        kbq_ent.cvss_temporal AS kbq_ent_cvss_tempor_5,
        kbq_ent.last_customization_user_login AS kbq_ent_last_custom_6,kbq_ent.last_customization_datetime AS kbq_ent_last_custom_7 
    FROM kbq_ent JOIN (SELECT vuln_eid AS vuln_eid, qid AS qid, anon_2.rel_eid AS anon_2_rel_eid 
    FROM (
            SELECT entity_vuln.entity_id AS vuln_eid,
                entity_vuln.qid AS qid 
            FROM entity_vuln
        ) JOIN (
            SELECT entity_responsible_org.entity_id AS rel_eid
            FROM entity_responsible_org 
            WHERE entity_responsible_org.org_id = :org_id_1
        ) anon_2 ON vuln_eid = anon_2.rel_eid) anon_1 ON kbq_ent.qid = anon_1.qid

`kbq_ent.solution AS kbq_ent_solution` is a CLOB.