<!-- 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,
return false;
    }
    
    if (IsWalletLoaded(wallet_path)) {
        error_string = Untranslated(strprintf("Error loading wallet %s. Duplicate -wallet filename specified.", location.GetName()));
        return false;
    }
    
    std::unique_ptr<WalletDatabase> database = CreateWalletDatabase(wallet_path);
    try {
        if (!WalletBatch::VerifyEnvironment(wallet_path, error_string)) {
            return false;
        }
    } catch (const fs::filesystem_error& e) {
        error_string = Untranslated(strprintf("Error loading wallet %s. %s", location.GetName(), fsbridge::get_filesystem_error_message(e)));
        return false;
    }
    return WalletBatch::VerifyDatabaseFile(wallet_path, error_string);
}
std::shared_ptr<CWallet> CWallet::CreateWalletFromFile(interfaces::Chain& chain, const WalletLocation& location, bilingual_str& error, std::vector<bilingual_str>& warnings, uint64_t wallet_creation_flags)
{
    const std::string walletFile = WalletDataFilePath(location.GetPath()).string();
    
    std::list<CWalletTx> vWtx;
    if (gArgs.GetBoolArg("-zapwallettxes", false)) {
        chain.initMessage(_("Zapping all transactions from wallet...").translated);
        std::unique_ptr<CWallet> tempWallet = MakeUnique<CWallet>(&chain, location, CreateWalletDatabase(location.GetPath()));
        DBErrors nZapWalletRet = tempWallet->ZapWalletTx(vWtx);
        if (nZapWalletRet != DBErrors::LOAD_OK) {
            error = strprintf(_("Error loading %s: Wallet corrupted"), walletFile);