Characters / Symbols Disappear after motion tween

Before updating to Animate 2021, I made a short animation where an animal sticks out its tongue, wiggles it in the air, then it goes back into its mouth. I saved the file, and exported a video draft as well.

Now that I've updated - when I go back to the file... the tongue disappears partly through the animation.

Within the document, the tongue was a .png file, in its own layer. I used the asset warp tool to pick anchors, then I "Created a Classic Tween" for the motion. 

Does anyone know why this is happening?