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.
fInternal = false;
            }
            try {
                READWRITE(m_pre_split);
            }
            catch (std::ios_base::failure&) {
                /* flag as postsplit address if we can't read the m_pre_split boolean
                   (this will be the case for any wallet that upgrades to HD chain split)*/
                m_pre_split = false;
            }
        }
        else {
            READWRITE(fInternal);
            READWRITE(m_pre_split);
        }
    }
};
/*
 * A class implementing ScriptPubKeyMan manages some (or all) scriptPubKeys used in a wallet.
 * It contains the scripts and keys related to the scriptPubKeys it manages.
 * A ScriptPubKeyMan will be able to give out scriptPubKeys to be used, as well as marking
 * when a scriptPubKey has been used. It also handles when and how to store a scriptPubKey
 * and its related scripts and keys, including encryption.
 */
class ScriptPubKeyMan
{
protected:
    WalletStorage& m_storage;
public:
    ScriptPubKeyMan(WalletStorage& storage) : m_storage(storage) {}