<!-- 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,
wtx.nTimeReceived = chain().getAdjustedTime();
        wtx.nOrderPos = IncOrderPosNext(&batch);
        wtx.m_it_wtxOrdered = wtxOrdered.insert(std::make_pair(wtx.nOrderPos, &wtx));
        wtx.nTimeSmart = ComputeTimeSmart(wtx);
        AddToSpends(hash);
    }
    if (!fInsertedNew)
    {
        if (confirm.status != wtx.m_confirm.status) {
            wtx.m_confirm.status = confirm.status;
            wtx.m_confirm.nIndex = confirm.nIndex;
            wtx.m_confirm.hashBlock = confirm.hashBlock;
            wtx.m_confirm.block_height = confirm.block_height;
            fUpdated = true;
        } else {
            assert(wtx.m_confirm.nIndex == confirm.nIndex);
            assert(wtx.m_confirm.hashBlock == confirm.hashBlock);
            assert(wtx.m_confirm.block_height == confirm.block_height);
        }
        
        
        
        
        
        if (tx->HasWitness() && !wtx.tx->HasWitness()) {
            wtx.SetTx(tx);
            fUpdated = true;
        }
    }