Problem: Layers have errors

hi,
i created an animation to use as teleram sticker, but the ‘telegram sticker export’ button shows error 'Layers have errors '. I don’t know what kind of error and therefore am not able to fix it- also i don’t have enough knowledge, as i am new to this.
what i did:
png files importet as footage - composition
adjusted the duration, converted into json
→ works as animation, although it flickers first but then shows smoothly.

could you help me with it?

…did I…say something wrong?