Are the yoga classes buggy?

Mine is exactly the same. Every time I do a class, the instructor starts the class and the Sims just stand there for ages. When they finally start taking part, they're out of sync with the instructor.

i dont even get that far its like the whole class goes by and then they do the final rest pose and thats it I'm like???? i hope it gets fixed!

I only got Spa Day a couple of weeks ago, so I don't know if it's a new bug or not. Hopefully it's fixed in the update that'll come before Island Living.

Mine is the same. Sometimes they stand there and watch the instructor or they actually do some moves, but they are one step behind the instructor.

sometimes they are a little behind, but I always thought this fitting, how could they be insync? they follow the instructor.
I had some npcs "join" the class only to leave it as soon as the instructor started...and if your sims has a low skilllevel in wellness, they will leave out some poses or do different easier poses instead.
But I never had all of them doing nothing so far.