<!-- 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,
int submitted_tx_count = 0;
    { 
        LOCK(cs_wallet);
        
        for (std::pair<const uint256, CWalletTx>& item : mapWallet) {
            CWalletTx& wtx = item.second;
            
            
            
            if (wtx.nTimeReceived > m_best_block_time - 5 * 60) continue;
            std::string unused_err_string;
            if (wtx.SubmitMemoryPoolAndRelay(unused_err_string, true)) ++submitted_tx_count;
        }
    } 
    if (submitted_tx_count > 0) {
        WalletLogPrintf("%s: resubmit %u unconfirmed transactions\n", __func__, submitted_tx_count);
    }
}
 
void MaybeResendWalletTxs()
{
    for (const std::shared_ptr<CWallet>& pwallet : GetWallets()) {
        pwallet->ResendWalletTransactions();
    }
}
/** @defgroup Actions
 *
 * @{
 */
CWallet::Balance CWallet::GetBalance(const int min_depth, bool avoid_reuse) const