<!-- 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 (IsLockedCoin(entry.first, i))
                continue;
            if (IsSpent(wtxid, i))
                continue;
            isminetype mine = IsMine(wtx.tx->vout[i]);
            if (mine == ISMINE_NO) {
                continue;
            }
            if (!allow_used_addresses && IsSpentKey(wtxid, i)) {
                continue;
            }
            std::unique_ptr<SigningProvider> provider = GetSolvingProvider(wtx.tx->vout[i].scriptPubKey);
            bool solvable = provider ? IsSolvable(*provider, wtx.tx->vout[i].scriptPubKey) : false;
            bool spendable = ((mine & ISMINE_SPENDABLE) != ISMINE_NO) || (((mine & ISMINE_WATCH_ONLY) != ISMINE_NO) && (coinControl && coinControl->fAllowWatchOnly && solvable));
            vCoins.push_back(COutput(&wtx, i, nDepth, spendable, solvable, safeTx, (coinControl && coinControl->fAllowWatchOnly)));
            
            if (nMinimumSumAmount != MAX_MONEY) {
                nTotal += wtx.tx->vout[i].nValue;
                if (nTotal >= nMinimumSumAmount) {
                    return;
                }
            }
            
            if (nMaximumCount > 0 && vCoins.size() >= nMaximumCount) {
                return;
            }
        }
    }
}
std::map<CTxDestination, std::vector<COutput>> CWallet::ListCoins() const