<!-- 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,
std::vector<OutputGroup> groups;
    std::map<CTxDestination, OutputGroup> gmap;
    std::set<CTxDestination> full_groups;
    for (const auto& output : outputs) {
        if (output.fSpendable) {
            CTxDestination dst;
            CInputCoin input_coin = output.GetInputCoin();
            size_t ancestors, descendants;
            chain().getTransactionAncestry(output.tx->GetHash(), ancestors, descendants);
            if (!single_coin && ExtractDestination(output.tx->tx->vout[output.i].scriptPubKey, dst)) {
                auto it = gmap.find(dst);
                if (it != gmap.end()) {
                    
                    
                    
                    
                    
                    if (it->second.m_outputs.size() >= OUTPUT_GROUP_MAX_ENTRIES) {
                        groups.push_back(it->second);
                        it->second = OutputGroup{};
                        full_groups.insert(dst);
                    }
                    it->second.Insert(input_coin, output.nDepth, output.tx->IsFromMe(ISMINE_ALL), ancestors, descendants);
                } else {
                    gmap[dst].Insert(input_coin, output.nDepth, output.tx->IsFromMe(ISMINE_ALL), ancestors, descendants);
                }