<!-- Describe the issue -->

Hi everyone,
We use bitcoin core with hundreds of wallets. The only efficient way we have found to do so is :
1. wait for any bitcoin-cli command to terminate before issuing another one
2. never issue any bitcoin-cli command unless tip update is 1
3. always unload a wallet after loading and using it

Now, we observ that bitcoin core systematically crashes every 20-30 minutes, then automatically restarts. And the problem is, it has to re-sync from about 0.997, which easily takes 15-20 minutes. During that time, the daemon cannot be used.

If we don't load/unload wallets, the daemon is stable and keeps to 1, no issue.

**System information**
Bitcoin Core RPC client version v0.20.0.0-ga62f0ed64f8bbbdfe6467ac5ce92ef5b5222d1bd
Compiled and run on Debian 9, on a VM with 16 mo memory. Launched that way : /bitcoind -daemon -walletrbf -conf=/root/.bitcoin/bitcoin.conf -fallbackfee=0.00001 -rpcworkqueue=128 -txindex=1

**bitcoin.conf :**
server=1
dbcache=16384
par=1
blocksonly=1
maxuploadtarget=137
maxconnections=16
rpcuser=bitcoinrpc
rpcpassword=xxxxxx
rpcallowip=127.0.0.1
testnet=0
txindex=1
walletbroadcast=1
txconfirmtarget=1

Please note that the same behaviour was happening with older releases (from 0.17.x).

Thanks for any help. Please ask for any needed information / testing.
Regards,
{
    WalletBatch batch(*database);
    return SetAddressBookWithDB(batch, address, strName, strPurpose);
}
bool CWallet::DelAddressBook(const CTxDestination& address)
{
    
    
    
    if (IsMine(address)) {
        WalletLogPrintf("%s called with IsMine address, NOT SUPPORTED. Please report this bug! %s\n", __func__, PACKAGE_BUGREPORT);
        return false;
    }
    {
        LOCK(cs_wallet);
        
        std::string strAddress = EncodeDestination(address);
        for (const std::pair<const std::string, std::string> &item : m_address_book[address].destdata)
        {
            WalletBatch(*database).EraseDestData(strAddress, item.first);
        }
        m_address_book.erase(address);
    }
    NotifyAddressBookChanged(this, address, "", IsMine(address) != ISMINE_NO, "", CT_DELETED);
    WalletBatch(*database).ErasePurpose(EncodeDestination(address));
    return WalletBatch(*database).EraseName(EncodeDestination(address));
}
size_t CWallet::KeypoolCountExternalKeys() const