Problem with constraint on timeline,Problem with position contraint on timeline

Hi. There's a problem when I animate the position constraint on the timeline. It was works fine until I reopen the project.

I create a game object to perform like hold on hand then toss away and fall to the ground, I animated in the timeline with position constraint or parent constraint, it works at the beginning, but when I reopen the project, some of the constraints will be lost, some still there. (Reference picture) I had made 4 empty objects for the position constraint(two on the animated characters and the other two are static objects), and if I don't close the unity, it went well. But once I close the project, it'll be lost. Any ideas on how to solve this issue?

,Hi. There's a problem when I animate the position constraint on the timeline. It was works fine until I reopen the project.

I create a game object to perform like hold on hand then toss away and fall to the ground, I animated in the timeline with position constraint or parent constraint, it works at the beginning, but when I reopen the project, some of the constraints will be lost, some still there. (Reference picture)

I had made 4 empty objects for the position constraint(two on the animated characters and the other two are static objects), and if I don't close the unity, it went well. But once I close the project, it'll be lost. Any ideas on how to solve this issue?