Reported here: https://github.com/bitcoin/bitcoin/pull/10244#issuecomment-378035305

Travis log here: https://travis-ci.org/bitcoin/bitcoin/jobs/361243719#L2810

Note the JSON exception:

```
test_framework.authproxy.JSONRPCException: The mempool was not loaded yet (-1) 
```

That exception was introduced here: https://github.com/bitcoin/bitcoin/commit/cb1e319fe9e198c9c5cf5236fe9af5a3d748b9e8#diff-a0c8f511d90e83aa9b5857e819ced344R1617

cc @jtimon 
AssertLockHeld(cs_main);
    int nHeight = pindex->nHeight;
    
    BlockMap::iterator it = mapBlockIndex.begin();
    while (it != mapBlockIndex.end()) {
        if (!it->second->IsValid() && it->second->GetAncestor(nHeight) == pindex) {
            it->second->nStatus &= ~BLOCK_FAILED_MASK;
            setDirtyBlockIndex.insert(it->second);
            if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && setBlockIndexCandidates.value_comp()(chainActive.Tip(), it->second)) {
                setBlockIndexCandidates.insert(it->second);
            }
            if (it->second == pindexBestInvalid) {
                
                pindexBestInvalid = nullptr;
            }
            m_failed_blocks.erase(it->second);
        }
        it++;
    }
    
    while (pindex != nullptr) {
        if (pindex->nStatus & BLOCK_FAILED_MASK) {
            pindex->nStatus &= ~BLOCK_FAILED_MASK;
            setDirtyBlockIndex.insert(pindex);
            m_failed_blocks.erase(pindex);
        }
        pindex = pindex->pprev;
    }
}
void ResetBlockFailureFlags(CBlockIndex *pindex) {