There are some potential feefilter cleanups mentioned and motivated in comment https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-805808485 . If you address the locking one, please be careful and make sure that `round()` is only called under a lock. See https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-807992199

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headers[0].hashPrevBlock.ToString(),
                    pindexBestHeader->nHeight,
                    pfrom.GetId(), nodestate->nUnconnectingHeaders);
            
            
            
            UpdateBlockAvailability(pfrom.GetId(), headers.back().GetHash());
            if (nodestate->nUnconnectingHeaders % MAX_UNCONNECTING_HEADERS == 0) {
                Misbehaving(pfrom.GetId(), 20, strprintf("%d non-connecting headers", nodestate->nUnconnectingHeaders));
            }
            return;
        }
        uint256 hashLastBlock;
        for (const CBlockHeader& header : headers) {
            if (!hashLastBlock.IsNull() && header.hashPrevBlock != hashLastBlock) {
                Misbehaving(pfrom.GetId(), 20, "non-continuous headers sequence");
                return;
            }
            hashLastBlock = header.GetHash();
        }
        
        
        if (!m_chainman.m_blockman.LookupBlockIndex(hashLastBlock)) {
            received_new_header = true;
        }
    }
    BlockValidationState state;
    if (!m_chainman.ProcessNewBlockHeaders(headers, state, m_chainparams, &pindexLast)) {
        if (state.IsInvalid()) {
            MaybePunishNodeForBlock(pfrom.GetId(), state, via_compact_block, "invalid header received");