<!-- 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,
}
    }
    const Optional<int> tip_height = chain.getHeight();
    if (tip_height) {
        walletInstance->m_last_block_processed = chain.getBlockHash(*tip_height);
        walletInstance->m_last_block_processed_height = *tip_height;
    } else {
        walletInstance->m_last_block_processed.SetNull();
        walletInstance->m_last_block_processed_height = -1;
    }
    if (tip_height && *tip_height != rescan_height)
    {
        
        
        
        if (chain.havePruned()) {
            
            
            
            int block_height = *tip_height;
            while (block_height > 0 && chain.haveBlockOnDisk(block_height - 1) && rescan_height != block_height) {
                --block_height;
            }
            if (rescan_height != block_height) {
                error = _("Prune: last wallet synchronisation goes beyond pruned data. You need to -reindex (download the whole blockchain again in case of pruned node)");
                return nullptr;
            }
        }
        chain.initMessage(_("Rescanning...").translated);
        walletInstance->WalletLogPrintf("Rescanning last %i blocks (from block %i)...\n", *tip_height - rescan_height, rescan_height);