<!-- 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,
error = strprintf(Untranslated("Wallet %s already exists."), location.GetName());
        return WalletCreationStatus::CREATION_FAILED;
    }
    
    if (!CWallet::Verify(chain, location, error, warnings)) {
        error = Untranslated("Wallet file verification failed.") + Untranslated(" ") + error;
        return WalletCreationStatus::CREATION_FAILED;
    }
    
    if (!passphrase.empty() && (wallet_creation_flags & WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        error = Untranslated("Passphrase provided but private keys are disabled. A passphrase is only used to encrypt private keys, so cannot be used for wallets with private keys disabled.");
        return WalletCreationStatus::CREATION_FAILED;
    }
    
    std::shared_ptr<CWallet> wallet = CWallet::CreateWalletFromFile(chain, location, error, warnings, wallet_creation_flags);
    if (!wallet) {
        error = Untranslated("Wallet creation failed.") + Untranslated(" ") + error;
        return WalletCreationStatus::CREATION_FAILED;
    }
    
    if (!passphrase.empty() && !(wallet_creation_flags & WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        if (!wallet->EncryptWallet(passphrase)) {
            error = Untranslated("Error: Wallet created but failed to encrypt.");
            return WalletCreationStatus::ENCRYPTION_FAILED;
        }
        if (!create_blank) {
            
            if (!wallet->Unlock(passphrase)) {
                error = Untranslated("Error: Wallet was encrypted but could not be unlocked");
                return WalletCreationStatus::ENCRYPTION_FAILED;