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.
{
    return ::SignTransaction(tx, this, coins, sighash, input_errors);
}
SigningResult LegacyScriptPubKeyMan::SignMessage(const std::string& message, const PKHash& pkhash, std::string& str_sig) const
{
    CKeyID key_id(pkhash);
    CKey key;
    if (!GetKey(key_id, key)) {
        return SigningResult::PRIVATE_KEY_NOT_AVAILABLE;
    }
    if (MessageSign(key, message, str_sig)) {
        return SigningResult::OK;
    }
    return SigningResult::SIGNING_FAILED;
}
TransactionError LegacyScriptPubKeyMan::FillPSBT(PartiallySignedTransaction& psbtx, int sighash_type, bool sign, bool bip32derivs) const