in v0.12 https://github.com/bitcoin/bitcoin/pull/7081 (by @luke-jr) was merged adding `-bytespersigop` (with default of 20).

this is preventing simple bare multisig transactions from being accepted into mempool when the size is < 400 bytes.  
eg; https://gist.github.com/rubensayshi/ac4f617207f7a50559e85d61c05800be

from 1-of-7 and onwards they are accepted because the ratio of bytes:sigops is high enough.  
also having 2 or more inputs will work because it again tips the ratio of bytes:sigops over.

the reason mainly being that `GetLegacySigOpCount` calls `GetSigOpCount` with `fAccurate=false`.

It looks like changing `GetLegacySigOpCount` to use `fAccurate=true` would cause side effects in the few other places (`ConnectBlock`, `CheckBlock`, `CreateNewBlock`) and simply adding `fAccurate` as arg to `GetLegacySigOpCount` would affect the value stored in `CTxMemPoolEntry.sigOpCount` which in turn affects a bunch of other things.

FILE *file = fopen(path.string().c_str(), "rb");
        if (file) {
            LogPrintf("Importing blocks file %s...\n", path.string());
            LoadExternalBlockFile(chainparams, file);
        } else {
            LogPrintf("Warning: Could not open blocks file %s\n", path.string());
        }
    }
    
    CValidationState state;
    if (!ActivateBestChain(state, chainparams)) {
        LogPrintf("Failed to connect best block");
        StartShutdown();
    }
    if (GetBoolArg("-stopafterblockimport", DEFAULT_STOPAFTERBLOCKIMPORT)) {
        LogPrintf("Stopping after block import\n");
        StartShutdown();
    }
}
/** Sanity checks
 *  Ensure that Bitcoin is running in a usable environment with all
 *  necessary library support.
 */
bool InitSanityCheck(void)