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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{
    std::shared_ptr<const CBlockHeaderAndShortTxIDs> pcmpctblock = std::make_shared<const CBlockHeaderAndShortTxIDs> (*pblock, true);
    const CNetMsgMaker msgMaker(PROTOCOL_VERSION);
    LOCK(cs_main);
    static int nHighestFastAnnounce = 0;
    if (pindex->nHeight <= nHighestFastAnnounce)
        return;
    nHighestFastAnnounce = pindex->nHeight;
    bool fWitnessEnabled = IsWitnessEnabled(pindex->pprev, m_chainparams.GetConsensus());
    uint256 hashBlock(pblock->GetHash());
    {
        LOCK(cs_most_recent_block);
        most_recent_block_hash = hashBlock;
        most_recent_block = pblock;