<!-- This issue tracker is only for technical issues related to Bitcoin Core.

General bitcoin questions and/or support requests are best directed to the Bitcoin StackExchange at https://bitcoin.stackexchange.com.

For reporting security issues, please read instructions at https://bitcoincore.org/en/contact/.

If the node is "stuck" during sync or giving "block checksum mismatch" errors, please ensure your hardware is stable by running memtest and observe CPU temperature with a load-test tool such as linpack before creating an issue! -->

<!-- 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. -->

#include <utility>
#include <vector>
bool VerifyWallets(interfaces::Chain& chain, const std::vector<std::string>& wallet_files);
bool LoadWallets(interfaces::Chain& chain, const std::vector<std::string>& wallet_files);
void StartWallets(CScheduler& scheduler);
void FlushWallets();
void StopWallets();
void UnloadWallets();
void UnloadWallet(std::shared_ptr<CWallet>&& wallet);
bool AddWallet(const std::shared_ptr<CWallet>& wallet);
bool RemoveWallet(const std::shared_ptr<CWallet>& wallet);
bool HasWallets();
std::vector<std::shared_ptr<CWallet>> GetWallets();
std::shared_ptr<CWallet> GetWallet(const std::string& name);
std::shared_ptr<CWallet> LoadWallet(interfaces::Chain& chain, const WalletLocation& location, std::string& error, std::string& warning);
static const unsigned int DEFAULT_KEYPOOL_SIZE = 1000;
constexpr CAmount DEFAULT_PAY_TX_FEE = 0;
static const CAmount DEFAULT_FALLBACK_FEE = 20000;
static const CAmount DEFAULT_DISCARD_FEE = 10000;
static const CAmount DEFAULT_TRANSACTION_MINFEE = 1000;
static const CAmount WALLET_INCREMENTAL_RELAY_FEE = 5000;
static const bool DEFAULT_SPEND_ZEROCONF_CHANGE = true;
static const bool DEFAULT_WALLET_REJECT_LONG_CHAINS = false;
static const bool DEFAULT_AVOIDPARTIALSPENDS = false;
static const unsigned int DEFAULT_TX_CONFIRM_TARGET = 6;
static const bool DEFAULT_WALLET_RBF = false;
static const bool DEFAULT_WALLETBROADCAST = true;
static const bool DEFAULT_DISABLE_WALLET = false;
static constexpr size_t DUMMY_NESTED_P2WPKH_INPUT_SIZE = 91;
class CCoinControl;