If I unlock an encrypted wallet for 359711509437336256 or less seconds, I can sign transactions with it:

    $ bitcoin-cli walletpassphrase "$x" 359711509437336256
    $ echo $?
    0
    $ bitcoin-cli signrawtransaction $tx | grep complete
      "complete": true

But if I unlock it for 359711509437336257 or more seconds, it appears to have unlocked but I can't sign any transactions:

    $ bitcoin-cli walletpassphrase "$x" 359711509437336257
    $ echo $?
    0
    $ bitcoin-cli signrawtransaction $tx | grep complete
    error code: -13
    error message:
    Error: Please enter the wallet passphrase with walletpassphrase first.

I don't know the significance of that number. It's nowhere near a power of 2.

I was trying to unlock the wallet effectively "forever", so put a big number. If I use too big a number (2^63 or more) I get an error message `JSON integer out of range` but for numbers between 359711509437336257 and 2^63-1 inclusive I get no error, but no actual unlocking.
"3. include_watchonly (bool, optional, default=false) Whether to include watch-only addresses (see 'importaddress').\n"
            "\nResult:\n"
            "[\n"
            "  {\n"
            "    \"involvesWatchonly\" : true,        (bool) Only returned if imported addresses were involved in transaction\n"
            "    \"address\" : \"receivingaddress\",  (string) The receiving address\n"
            "    \"account\" : \"accountname\",       (string) DEPRECATED. The account of the receiving address. The default account is \"\".\n"
            "    \"amount\" : x.xxx,                  (numeric) The total amount in " + CURRENCY_UNIT + " received by the address\n"
            "    \"confirmations\" : n,               (numeric) The number of confirmations of the most recent transaction included\n"
            "    \"label\" : \"label\",               (string) A comment for the address/transaction, if any\n"
            "    \"txids\": [\n"
            "       n,                                (numeric) The ids of transactions received with the address \n"
            "       ...\n"
            "    ]\n"
            "  }\n"
            "  ,...\n"
            "]\n"
            "\nExamples:\n"
            + HelpExampleCli("listreceivedbyaddress", "")
            + HelpExampleCli("listreceivedbyaddress", "6 true")
            + HelpExampleRpc("listreceivedbyaddress", "6, true, true")
        );
    ObserveSafeMode();
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    LOCK2(cs_main, pwallet->cs_wallet);
    return ListReceived(pwallet, request.params, false);
}
UniValue listreceivedbyaccount(const JSONRPCRequest& request)