<!-- 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,
break;
            }
            
            block_hash = next_block_hash;
            ++block_height;
            progress_current = chain().guessVerificationProgress(block_hash);
            
            const uint256 prev_tip_hash = tip_hash;
            tip_hash = WITH_LOCK(cs_wallet, return GetLastBlockHash());
            if (!max_height && prev_tip_hash != tip_hash) {
                
                progress_end = chain().guessVerificationProgress(tip_hash);
            }
        }
    }
    ShowProgress(strprintf("%s " + _("Rescanning...").translated, GetDisplayName()), 100); 
    if (block_height && fAbortRescan) {
        WalletLogPrintf("Rescan aborted at block %d. Progress=%f\n", block_height, progress_current);
        result.status = ScanResult::USER_ABORT;
    } else if (block_height && chain().shutdownRequested()) {
        WalletLogPrintf("Rescan interrupted by shutdown request at block %d. Progress=%f\n", block_height, progress_current);
        result.status = ScanResult::USER_ABORT;
    } else {
        WalletLogPrintf("Rescan completed in %15dms\n", GetTimeMillis() - start_time);
    }
    return result;
}
void CWallet::ReacceptWalletTransactions()