Tween Goes Crazy Then Returns to Where I asked it go on Final Keyframe Only.

[pete142]

I am new to using Adobe Animate but this was working fine until today. I had to re-do a character's eyes on a long timeline. Whenever I tween his pupil movements, it goes crazy, then snaps back to where I actually asked it to go on the last keyframe. The pupils are parented to the eyes and the eyes are parented to the head, which is tilting-- but I don't understand why it's drifting away as it tweens like this.

I have tried setting up a new layer to work on, tried using the paintbrush or the oval tool to create the black pupils again and again. But it keeps doing it. Thanks!

[_keyframer]

You must cover your art to a symbol before tweening. 
Always have 1 symbol per tween.

 Make sure the center point never changes across key frames in a tween. Check the center point using the Free Transform tool. Select the symbol and look for the white dot. If it's in different locations between key frames, the symbol will drift. To fix it, double click the white dot to snap it to the symbol's internal center point for every key frame and it should no longer drift.