When running walletpassphrase on a large wallet.dat (ie about 300,000 segwit P2SH addresses) the command sometimes takes a very long time, and if command is run multiple times at once (while running slow) it causes bitcoin core to freeze (stops syncing and requires kill -9 to stop/restart)

During the locked up walletpassphrase commands being run the following messages start to appear in the debug.log:

`018-01-24 01:01:04 socket sending timeout: 1201s`

Note that this problem is intermittent, so sometimes the command runs instantly, other times it takes a few minutes, and other times it completely freezes the node.
{
    if (!WriteIC(std::make_pair(DBKeys::WATCHMETA, dest), keyMeta)) {
        return false;
    }
    return WriteIC(std::make_pair(DBKeys::WATCHS, dest), '1');
}
bool WalletBatch::EraseWatchOnly(const CScript &dest)
{
    if (!EraseIC(std::make_pair(DBKeys::WATCHMETA, dest))) {
        return false;
    }
    return EraseIC(std::make_pair(DBKeys::WATCHS, dest));
}
bool WalletBatch::WriteBestBlock(const CBlockLocator& locator)
{
    WriteIC(DBKeys::BESTBLOCK, CBlockLocator()); 
    return WriteIC(DBKeys::BESTBLOCK_NOMERKLE, locator);
}
bool WalletBatch::ReadBestBlock(CBlockLocator& locator)
{
    if (m_batch.Read(DBKeys::BESTBLOCK, locator) && !locator.vHave.empty()) return true;
    return m_batch.Read(DBKeys::BESTBLOCK_NOMERKLE, locator);
}
bool WalletBatch::WriteOrderPosNext(int64_t nOrderPosNext)
{
    return WriteIC(DBKeys::ORDERPOSNEXT, nOrderPosNext);
}
bool WalletBatch::ReadPool(int64_t nPool, CKeyPool& keypool)