<!-- 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,
WalletLogPrintf("AddToWallet %s  %s%s\n", hash.ToString(), (fInsertedNew ? "new" : ""), (fUpdated ? "update" : ""));
    
    if (fInsertedNew || fUpdated)
        if (!batch.WriteTx(wtx))
            return nullptr;
    
    wtx.MarkDirty();
    
    NotifyTransactionChanged(this, hash, fInsertedNew ? CT_NEW : CT_UPDATED);
#if HAVE_SYSTEM
    
    std::string strCmd = gArgs.GetArg("-walletnotify", "");
    if (!strCmd.empty())
    {
        boost::replace_all(strCmd, "%s", hash.GetHex());
#ifndef WIN32
        
        
        
        
        
        boost::replace_all(strCmd, "%w", ShellEscape(GetName()));
#endif
        std::thread t(runCommand, strCmd);
        t.detach(); 
    }
#endif
    return &wtx;
}
bool CWallet::LoadToWallet(const uint256& hash, const UpdateWalletTxFn& fill_wtx)