My tiel will be 9 later this year and has always been a big fan of millet spray and treats - until recently. Lately he started to prefer loose seeds and mostly ignores treats and even millet spray!
He is healthy and has a good appetite.
Would could the cause be?

Obviously when he had eaten about 3/4 of the treat the treat fell off (detached itself from the stick), which scared him sometimes, but this was nothing new. It had happened many times and he still loved treats.

Any ideas? Has this happened to anybody else?

Maybe he's just tired of these things? My birds go through seasonal changes in what they want to eat. You can try not offering these things for a while, and then maybe it'll seem like something special when you bring them back.

Thank you, I will try that. I have indeed spoiled quite a bit lately, and maybe he just got tired of treats.

One way to make treats special is to never just have them sitting around in the cage like ordinary food. Make it something that he only gets when he's directly interacting with you. Like eating from your hand, or doing something cute that you want to encourage.

I'll try that. He loves attention, so maybe he needs more when getting a treat. He used to literally jump on my hand when I gave him one while I was putting it in the cage, that's how much he liked them.
I will try to give him less and with more attention and love.

Animals get burned out of things. My gecko recently went on a kick where she would deny food if it wasn't wax worms, which is kind of a fatty treat, not really healthy. Put a mealworm or cricket in front of her and she would ignore it. Now she'll eat both again. Different preferences at different times. He doesn't dislike it, but needs some new treats.

Yesterday he ate some millet... He is still just sitting on his treat.

Yes, I guess there is nothing wrong with my baby. I will just see what happens.
Maybe he is like a kid getting tired of toys or too much chocolate.

We humans change our tastes too sometimes. I had periods where I loved milk and cereals for example, then I got tired of cereals (without a specific reason), and now I like them again.

Sometimes we just need a break...

my bird loves safflour seed and hemp. i dont give alot seed but he dont like millet at all.

Hemp is a very nutritious seed - it's got lots of protein in it, and Omega 3 fatty acids. It's an oil seed so it's high in fat, so don't go crazy with it. But it's the best of the oil seeds.

its mostly as a treat he only gets seed for training and once or twice a wk in a bowl.