Hello everybody,
so here is a history of a spades round, with some of my comments:
Note that this is a team game with 4 players, and I will also skip the non interesting tricks:
Of course, I don't expect bots to be perfect at all, but a nill should be very simple and easy to follow and play.
Round #17.
It's Sonic's turn.
Sonic thinks taking 0 tricks this round.
It's Anastasia's turn.
Anastasia thinks taking 3 tricks this round.
It's your turn.
Press B to enter the number of tricks you think you will take in this round.
You think you will take 3 tricks this round.
It's Newby computer's turn.
Newby computer thinks taking 4 tricks this round.
Here it started with a few basic tricks, but the important suits are especially diamonds and spades.
Nikola plays an ace of diamonds.
It's Newby computer's turn.
Newby computer plays a 2 of diamonds.
It's Sonic's turn.
Sonic plays a 5 of diamonds.
It's Anastasia's turn.
Anastasia plays a 3 of diamonds.
Nikola wins the trick.
It's your turn.
Nikola plays a 7 of diamonds.
It's Newby computer's turn.
Newby computer plays a 4 of diamonds.
It's Sonic's turn.
Sonic plays an 8 of diamonds.
It's Anastasia's turn.
Anastasia plays a 10 of diamonds.
Anastasia wins the trick.
It's Anastasia's turn.
Now, the logical thing would of course be that Sonic plays his 8, being that I took out my ace and he could play his highest card.
But, if only that was the end...
Nikola plays a 6 of diamonds.
It's Newby computer's turn.
Newby computer plays a 5 of spades.
It's Sonic's turn.
Sonic plays a queen of diamonds.
It's Anastasia's turn.
Anastasia plays a king of diamonds.
Newby computer wins the trick.
It's Newby computer's turn.
So, as you can see, he plays his lowest card on the ace, but in reality has a queen.
Then, this entire nill is questionable, especially if we look at the spades played:
Newby computer plays a 7 of spades.
It's Sonic's turn.
Sonic plays an 8 of spades.
It's Anastasia's turn.
Anastasia plays a 2 of spades.
It's your turn.
Nikola plays a 10 of spades.
Nikola wins the trick.
It's your turn.
Nikola plays a 10 of hearts.
It's Newby computer's turn.
Newby computer plays a queen of spades.
It's Sonic's turn.
Sonic plays a 9 of spades.
It's Anastasia's turn.
Anastasia plays a 4 of spades.
Newby computer wins the trick.
It's Newby computer's turn.
Newby computer plays an ace of spades.
It's Sonic's turn.
ace of spades, Newby computer
Sonic plays a king of spades.
It's Anastasia's turn.
Anastasia plays a jack of spades.
It's your turn.
Nikola plays a 3 of spades.
Newby computer wins the trick.

I don't understand how the bots are created to understand this as a good nill to play. Not only this, but really playing a nill should be relatively simple to program. All the bot has to do is play the highest cards possible without winning a trick, thus if an ace is on the table, logically play his strongest card of the suit.
In addition to that, play a nill with a king of spades in very rare conditions, especially not with 2 more high spades.
Hopefully their logic of both bidding and playing a nill can be improved in the future.

Seems like it doesn't consider nil as a special case. It just thinks it can get 0 tricks and get whatever it can anyway.

This has happened once before but I would say a rare bug.

I've seen bots betting 0 with an ace of spades several times, I think this is the one that should be really solved.

Nah not really rare, also they should learn how to protect zero. Few if elses, and should be fine :)

From the sounds of this the issue is the ace of spades not the other aces as bots don't always bet 0 when they have other aces.

I doubt it is rare as well, and while I can't say I seen the ace of spades case, if that is true then indeed that is especially a priority.
However, as you can see, not only aces are problematic, rather that they don't know or as RedHawk rightly says don't have any special case for playing a nill and just seem to play it as any other round.
It's also true that covering a nill of your partner should be improved.

Hello,

It should be slightly better from today's update on. Tell me if it really is, or if my fix didn't change anything.

Bots should no longer nil bid if they have any spade figure or if they think they can make more than 2 tricks. They should also be more keen to go nil if they are behind in score.

Hello Aminiel, not sure if they should bid nill only if they have no spades, it is quite rare, rather set some condition, no higher than jack and not more than 3 spades, they also should not bid nill when they have only 3 pieces of a color and one of them is ace.
And here I give you another thing which annoys me even more than the nill thing because it occurs in every round.
Kiss plays a queen of hearts.
It's Robotnick's turn.
Robotnick plays a 3 of spades.
It's Thinky winky's turn.
Thinky winky plays a 7 of diamonds.
It's Violet duck's turn.
Violet duck plays a 7 of hearts.
Robotnick wins the trick.

As you can see my partner teletubby does not want to cut his opponent, it is funny because opponents don't hesitate to cut us. You should have a look at this because no matter what, bot partner won't cut the opponent, even if my partner got only spades left, let's say 3 4 10 and king, my opponent cut with 8 he will play 4 and undercut.
Note that this doesn't happen after bot took his tricks or we took our contract, it happens literally always.