If there's no health reason suspected, it can happen that a poodle suddenly will turn up their nose at a formerly enjoyed food. PTP's suggestion of a variety of same brand flavors is a good starting point. Transitioning is gradual, taking a few days, up to a week, so that slows things down a bit.
It's not usually recommended to do a lot of short term switching til they prove their cast iron stomach status, but Rotation Feeding is something worth looking into.
My Remo had been a fairly reluctant eater, tho he would eat, until I found a food that he realllly likes. When I open a bag of a new food, I see if he shows any interest in the plain kibble and he practically inhaled it this last time. Now he's as anxious as his brother for me to get the food down dangit woman! Took me almost 3 years to find a food he wants to eat. I felt so bad about that.
Depending on where you buy the food, many places will take the food back if it's not a hit in the first week or so. I don't know if these kinds of things will start up again but PetSmart had occasional Sample Saturdays for various brands, and a few brands offer bagged trial size regularly. At least they used to.
So long as it isn't a health issue, it's just going to be careful trial and error til you hit a winner or several.