I measured this on a test app with a calibration grid (I build Headloop, a tool for header and search videos). In the App Store Connect preview, on iPhone in portrait, the header is shown in a box of about 1.51:1 and the 21:9 video is scaled to fill it, so about 17.6% of the width is cut off on each side. The full height shows. Two live product pages on an iPhone 15 with iOS 27.0.1 used the same crop as the preview. What do you see on the iPhone 17: is the video stretched, or cropped differently from the preview? That would tell whether the 17 lays out the header differently.

Disclosure: I build Headloop, a tool for App Store header and search videos. The results below come from our own test uploads. On October 12, 2026 we uploaded 17 files to the Asset Library of a test app through the App Store Connect API, then polled each one until it reached a final state. Three were 3840 × 2560 search results videos. All three were processed and matched to the search results spec: Codec Profile / level Frame rate Length Audio Size H.264 High, 6.0 30 fps 16 s none 75.8 MB H.264 High, 6.0 30 fps 15 s yes 71.5 MB HEVC Main 30 fps 15 s yes 24.1 MB   The first file was built to match the example in your post. So in our tests, the resolution, codec, profile, level, frame rate, length and missing audio track of your example did not cause POST_PROCESSING_FAILED on their own. The difference we can see is size. Our 16 s file averages about 38 Mbit/s. Your exports average about 1 Mbit/s (2 MB) and about 10 Mbit/s (19.2 MB). That is one data point, not a proven cause, and Apple publishes no bitrate requirement. What this doesn't cover: we only checked processing. Nothing was submitted to App Review or placed on a product page. I have no information on the deletion error (STATE_ERROR.ASSET_PREVIOUSLY_SUBMITTED_FOR_REVIEW).