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<!-- Describe the issue -->
Have two wallets used by this instance of bitcoind. The default wallet has balance 0.02861762.
Initially reported balance is correct but after unloading the wallet and then loading it again, the balance is wrong. Neither of the wallets have the reported balance.
<!--- What behavior did you expect? -->
I expected the balance to be the same as initially reported.
```
btc@ubuntu:~$ bitcoin-cli  -getinfo
{
  "version": 170100,
  "protocolversion": 70015,
  "walletversion": 159900,
  "balance": 0.02861762,
...

btc@ubuntu:~$ bitcoin-cli  loadwallet wallet2
btc@ubuntu:~$ bitcoin-cli unloadwallet ""
btc@ubuntu:~$ bitcoin-cli loadwallet ""
btc@ubuntu:~$ bitcoin-cli unloadwallet wallet2
btc@ubuntu:~$ bitcoin-cli  -getinfo
{
  "version": 170100,
  "protocolversion": 70015,
  "walletversion": 159900,
  "balance": 0.01012607,
...
```
The balance 0.01012607 is wrong and I have no idea where that number came from.
Restarting the process results in correct balance again.
<!--- What was the actual behavior (provide screenshots if the issue is GUI-related)? -->

<!--- How reliably can you reproduce the issue, what are the steps to do so? -->

<!-- What version of Bitcoin Core are you using, where did you get it (website, self-compiled, etc)? -->
ubuntu package for bionic
<!-- What type of machine are you observing the error on (OS/CPU and disk type)? -->

<!-- For the GUI-related issue on Linux provide names and versions of a distro, a desktop environment and a graphical shell (if relevant). -->

<!-- Any extra information that might be useful in the debugging process. -->
<!--- This is normally the contents of a `debug.log` or `config.log` file. Raw text or a link to a pastebin type site are preferred. -->

{
    if (data.exists("timestamp")) {
        const UniValue& timestamp = data["timestamp"];
        if (timestamp.isNum()) {
            return timestamp.get_int64();
        } else if (timestamp.isStr() && timestamp.get_str() == "now") {
            return now;
        }
        throw JSONRPCError(RPC_TYPE_ERROR, strprintf("Expected number or \"now\" timestamp value for key. got type %s", uvTypeName(timestamp.type())));
    }
    throw JSONRPCError(RPC_TYPE_ERROR, "Missing required timestamp field for key");
}
UniValue importmulti(const JSONRPCRequest& mainRequest)
{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(mainRequest);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, mainRequest.fHelp)) {
        return NullUniValue;
    }
    if (mainRequest.fHelp || mainRequest.params.size() < 1 || mainRequest.params.size() > 2)
        throw std::runtime_error(
            RPCHelpMan{"importmulti",
                "\nImport addresses/scripts (with private or public keys, redeem script (P2SH)), optionally rescanning the blockchain from the earliest creation time of the imported scripts. Requires a new wallet backup.\n"
                "If an address/script is imported without all of the private keys required to spend from that address, it will be watchonly. The 'watchonly' option must be set to true in this case or a warning will be returned.\n"
                "Conversely, if all the private keys are provided and the address/script is spendable, the watchonly option must be set to false, or a warning will be returned.\n"
            "\nNote: This call can take over an hour to complete if rescan is true, during that time, other rpc calls\n"
            "may report that the imported keys, addresses or scripts exists but related transactions are still missing.\n",
                {
                    {"requests", RPCArg::Type::ARR, RPCArg::Optional::NO, "Data to be imported",