In the log I see things like:

    2017-09-13 03:54:33 init message: Rescanning...
    2017-09-13 03:54:33 Rescanning last 68616 blocks (from block 416339)...
    2017-09-13 03:54:40 AddToWallet xxxxx  update
    2017-09-13 03:55:33 Still rescanning. At block 418849. Progress=0.549138

I would be interested to see the wallet file name on each of these log lines.

Would there be any interest in merging such a PR?
CAmount& old_fee, CAmount& new_fee, CMutableTransaction& mtx)
{
    LOCK2(cs_main, wallet->cs_wallet);
    errors.clear();
    auto it = wallet->mapWallet.find(txid);
    if (it == wallet->mapWallet.end()) {
        errors.push_back("Invalid or non-wallet transaction id");
        return Result::INVALID_ADDRESS_OR_KEY;
    }
    const CWalletTx& wtx = it->second;
    Result result = PreconditionChecks(wallet, wtx, errors);
    if (result != Result::OK) {
        return result;
    }
    
    
    int nOutput = -1;
    for (size_t i = 0; i < wtx.tx->vout.size(); ++i) {
        if (wallet->IsChange(wtx.tx->vout[i])) {
            if (nOutput != -1) {
                errors.push_back("Transaction has multiple change outputs");
                return Result::WALLET_ERROR;
            }