Chicken stacked Minecart ignoring Attributes - movementSpeed

When I set speed to 10, it works. But not works if set to 0

Try something like 0.000000001

It moves that I can see.

Can confirm, relates to MC-14 and https://www.youtube.com/watch?v=GA2oSIMeFQE

It's not ignoring the data tag, it's that the Minecart is pushing the chicken around. Basically MC-14, as @unknown said. If you interrupt the movement, such as by surrounding it with blocks, the chicken's movementSpeed will take over again. I've got a chicken running around in circles at high speed with a minecart on its head, using the command in the description. So the real issue here is that the minecart is affecting the movement of the entity it's riding.

For example, try this:

summon Minecart ~ ~1 ~ {Riding:{id:Chicken, Riding:{id:Chicken, Attributes:[{Name:generic.movementSpeed, Base:3.0f}]}}}

The chicken will move at high speed, as expected, because the minecart isn't directly riding the chicken on the bottom of the stack, and thus won't override its movement.

The underlying issue is described in MC-38278, so marking this as a duplicate, and updating the other issue.