<!-- 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 (pwallet == nullptr)
        return 0;
    
    bool allow_cache = (filter & ISMINE_ALL) && (filter & ISMINE_ALL) != ISMINE_ALL;
    
    if (IsImmatureCoinBase())
        return 0;
    if (fUseCache && allow_cache && m_amounts[AVAILABLE_CREDIT].m_cached[filter]) {
        return m_amounts[AVAILABLE_CREDIT].m_value[filter];
    }
    bool allow_used_addresses = (filter & ISMINE_USED) || !pwallet->IsWalletFlagSet(WALLET_FLAG_AVOID_REUSE);
    CAmount nCredit = 0;
    uint256 hashTx = GetHash();
    for (unsigned int i = 0; i < tx->vout.size(); i++)
    {
        if (!pwallet->IsSpent(hashTx, i) && (allow_used_addresses || !pwallet->IsSpentKey(hashTx, i))) {
            const CTxOut &txout = tx->vout[i];
            nCredit += pwallet->GetCredit(txout, filter);
            if (!MoneyRange(nCredit))
                throw std::runtime_error(std::string(__func__) + " : value out of range");
        }
    }
    if (allow_cache) {
        m_amounts[AVAILABLE_CREDIT].Set(filter, nCredit);
        m_is_cache_empty = false;
    }
    return nCredit;
}
CAmount CWalletTx::GetImmatureWatchOnlyCredit(const bool fUseCache) const