I just tried to take a couple to a restaurant on a date. The food took forever to come in and the chef seemingly glitched mid cook. Their arms went out straight and then they started cooking the dish all over. Then when I sent the same sim to the food festival, I tried to have them take food from the buffet or food stand and they wouldn't take it. Their arms went out straight and nothing. This only happens on community lots, but not in the ski neighbourhood.
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You may have more going on than what I'm going to address, but let me start by saying, restaurants can be problematic.
I had downloaded Chez Lama, and when I place it, I discovered that I placed it backwards so that you had to walk around the back to enter the main entrance. I eventually had to re-build and call it "Casa de Lama."
In the rebuild, I opened up pathways, so wait-staff can get to and from the kitchen without bottlenecks. I learned that the placement of objects connected to the cooking and serving process had to be re-evaluated: the trash can was outside and around the building, so any time the waiter bussed the table, he'd get lost in the backyard.
Also... I discovered I had to eliminate the activity objects that aren't directly associated with food service/preparation. The NPC sims otherwise will become distracted during your meal and go play darts, for example.
Also, if you've just placed a new restaurant (without [Open for Business] ownership control of the staffing), I think that the sims assigned to the lot have to develop / train in the skill set associated with food service before they become proficient.
Look. that's just my take on it. I could be completely wrong.
Have fun.
@pjericksim I never thought of this. If you cheated their skills with MCC would that work?
http://www.getfreeebooks.com/star-trek-original-series-fan-fiction-trilogy/
Purely anecdotal, but it does seem to have helped in my game a lot.
But I always make sure my restaurants are laid out spaciously and if you have 2 chef stations and 2 waiters it speeds things up.