Reported here https://github.com/bitcoin/bitcoin/pull/12629#issuecomment-381095603 by @Empact.  I've seen it now in a few different travis jobs, including:

https://travis-ci.org/bitcoin/bitcoin/jobs/366157920
https://travis-ci.org/bitcoin/bitcoin/jobs/366139851

From my initial investigation it seems like there may be an actual bug in block announcement, so I'm  opening this issue to track.
if (pa->nChainWork > pb->nChainWork) return false;
            if (pa->nChainWork < pb->nChainWork) return true;
            
            if (pa->nSequenceId < pb->nSequenceId) return false;
            if (pa->nSequenceId > pb->nSequenceId) return true;
            
            
            if (pa < pb) return false;
            if (pa > pb) return true;
            
            return false;
        }
    };
} 
enum DisconnectResult