A defect in code added to support QNAME minimization can cause named to exit with an assertion failure if a forwarder returns a referral rather than resolving the query. This affects BIND versions 9.14.0 up to 9.14.6, and 9.15.0 up to 9.15.4.
https://support.f5.com/csp/article/K42238532?utm_source=f5support&%3Butm_medium=RSS