The final image does not open

I have created a complex Picture (Frame) with several overlapping shadows, objects, text, background, water droplets, etc., but when I export it in all formats, it appears with black bars, and in the Preview, the file contains mixed pixels instead of my original image. However, when I open it in the online version, the preview displays the correct image, and there are no black bars when I export the file. Can you help me understand why this is happening?