Problems with Black and White Party

Added

The caterer I hired would never cook anything even with all the needed items on the lot.

On any party or specifically the black/white party ?

That has only happened with the black and white party.

OK. Thanks

The caterer I hired managed to get to the "Stirring Bowl" animation, then stopped. 
Then she repeated it 3 more times, so I had 4 half made group items.

When I checked what it was, the caterer was making pancakes. All were pancakes, which was not needed for the objective lol.  

A few other problems with black and white parties:

1. The playing chess objective applies 'only' to the first, cheapest chessboard (i.e. the one that's black and white itself). The other chessboards don't count. Either the description needs updating or the objective should be able to be satisfied with other chessboards.

2. The 'listen to classical music with 3 sims at once' is not correctly working. Note that this was attempted with musicians who had the appreciate interaction and not the listen interaction. The objective log registers 1 sim listening when you choose 'appreciate classical music' but if in a conversation with 2 other sims and the action 'appreciate classical music together' is selected, the log resets to 0 sims listening. Attempted the same with 2 household sims in a conversation together, and the log will register 2 sims listening if both are listening to classical independently, but if one initiates conversation with the other and chooses to listen/appreciate classical music together, the log resets to 0 sims listening. Either the interaction is flawed, or the objective list isn't registering the group interaction correctly.

To add on to the caterer not cooking.  I had my sim throw a Black & White party to complete the 'Make 5 gourmet meals at a single event' part of the cooking aspiration.  She could not cook pretty much anything. I got a routing failure and the action would drop.  I created a 2nd test kitchen elsewhere in my house and managed to get her to cook a black & white cake, but couldn't use that kitchen again afterwards.  I tried resetting the sim, didn't help. Tried leaving her in a room with nothing but a counter, a stove, and a fridge and removing the door so other sims couldn't interfer, didn't help.  The issue persisted after I ended the party early.  She still couldn't cook.  I had another sim attempt to cook after the party ended and they were fine.  I fixed the issue for my main sim by travelling to another lot and back.  Only ever had this issues so far with the Black & White party specifically

The task "Make shrimp cocktail" is unachievable!

The task to have 3 sims listen to the piano simultaneously doesn´t work for me. Clicking the sim who plays and chose "Watch" seeing as there is no other option on the sim or the piano itself doesn´t count as "listen".