Common reasons:

• File too large – profile/cover images have a size limit (e.g., 2–8 MB depending on the slot). Oversized files may fail.
• Unsupported format – use standard formats like JPG/PNG/WEBP.
• Very low resolution – if the original is small and you stretch it, it will look blurry or pixelated.
• Heavy compression – screenshots/exported images with strong compression can look soft after upload.

Try this: use a clear, high-resolution image (preferably square for avatars, 1:1 crop if required), under the size limit, and re-upload.