<!-- 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,
if (!ParseMoney(gArgs.GetArg("-paytxfee", ""), nFeePerK)) {
            error = AmountErrMsg("paytxfee", gArgs.GetArg("-paytxfee", ""));
            return nullptr;
        }
        if (nFeePerK > HIGH_TX_FEE_PER_KB) {
            warnings.push_back(AmountHighWarn("-paytxfee") + Untranslated(" ") +
                               _("This is the transaction fee you will pay if you send a transaction."));
        }
        walletInstance->m_pay_tx_fee = CFeeRate(nFeePerK, 1000);
        if (walletInstance->m_pay_tx_fee < chain.relayMinFee()) {
            error = strprintf(_("Invalid amount for -paytxfee=<amount>: '%s' (must be at least %s)"),
                gArgs.GetArg("-paytxfee", ""), chain.relayMinFee().ToString());
            return nullptr;
        }
    }
    if (gArgs.IsArgSet("-maxtxfee")) {
        CAmount nMaxFee = 0;
        if (!ParseMoney(gArgs.GetArg("-maxtxfee", ""), nMaxFee)) {
            error = AmountErrMsg("maxtxfee", gArgs.GetArg("-maxtxfee", ""));
            return nullptr;
        }
        if (nMaxFee > HIGH_MAX_TX_FEE) {
            warnings.push_back(_("-maxtxfee is set very high! Fees this large could be paid on a single transaction."));
        }
        if (CFeeRate(nMaxFee, 1000) < chain.relayMinFee()) {
            error = strprintf(_("Invalid amount for -maxtxfee=<amount>: '%s' (must be at least the minrelay fee of %s to prevent stuck transactions)"),
                gArgs.GetArg("-maxtxfee", ""), chain.relayMinFee().ToString());
            return nullptr;
        }
        walletInstance->m_default_max_tx_fee = nMaxFee;