If you cast Lethal Scheme for its full convoke cost, each creature will connive, but the number of counters to add is additive. For example, if you connive discarding two nonland cards, then one land, then another nonland, the first creature will get one +1/+1 counter, the second and third two +1/+1 counters, and the last three +1/+1 counters. The intended behavior would be the first, second, and fourth each getting one +1/+1 counter with the third getting none.
This game has the case where four nonlands are discarded, but I've confirmed it works as described in single player: Game #843739446
This game has the case where four nonlands are discarded, but I've confirmed it works as described in single player: Game #843739446