<!-- 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,
} else if (wallet_creation_flags & WALLET_FLAG_DISABLE_PRIVATE_KEYS) {
        
        error = strprintf(_("Error loading %s: Private keys can only be disabled during creation"), walletFile);
        return NULL;
    } else if (walletInstance->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        for (auto spk_man : walletInstance->GetActiveScriptPubKeyMans()) {
            if (spk_man->HavePrivateKeys()) {
                warnings.push_back(strprintf(_("Warning: Private keys detected in wallet {%s} with disabled private keys"), walletFile));
                break;
            }
        }
    }
    if (!gArgs.GetArg("-addresstype", "").empty() && !ParseOutputType(gArgs.GetArg("-addresstype", ""), walletInstance->m_default_address_type)) {
        error = strprintf(_("Unknown address type '%s'"), gArgs.GetArg("-addresstype", ""));
        return nullptr;
    }
    if (!gArgs.GetArg("-changetype", "").empty() && !ParseOutputType(gArgs.GetArg("-changetype", ""), walletInstance->m_default_change_type)) {
        error = strprintf(_("Unknown change type '%s'"), gArgs.GetArg("-changetype", ""));
        return nullptr;
    }
    if (gArgs.IsArgSet("-mintxfee")) {
        CAmount n = 0;
        if (!ParseMoney(gArgs.GetArg("-mintxfee", ""), n) || 0 == n) {
            error = AmountErrMsg("mintxfee", gArgs.GetArg("-mintxfee", ""));
            return nullptr;
        }
        if (n > HIGH_TX_FEE_PER_KB) {
            warnings.push_back(AmountHighWarn("-mintxfee") + Untranslated(" ") +
                               _("This is the minimum transaction fee you pay on every transaction."));
        }