Persistent scroll stutter on iPhone 17 Pro Max, 18 Pro Max and 18 Pro (iOS 27.2), also on Apple Store demo units

UI Frameworks UIKit
WilliamPhilips OP
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Affected devices (all show the same problem):

  • 1x iPhone 17 Pro Max
  • 2x iPhone 18 Pro Max
  • 1x iPhone 18 Pro
  • Many demo iPhones at several Apple Stores
    Current iOS version: 27.2

Issue:
Vertical scrolling inside apps frequently stutters and drops frames. It happens in many, many apps, including Apple's own App Store and Apple Store apps. During a normal flick-and-decelerate scroll, the content repeatedly freezes for one or more frames and then jumps forward.

Because this reproduces on four of my own devices and on many Apple Store demo units, I believe it is a widespread, system-level issue, not a defect of a single device or my settings.

Impact:
I have been living with this for more than six months. I use my iPhone heavily every day, and the constant stutter has made using it genuinely distressing. Everything else about iPhone feels excellent, which makes this problem even harder to accept.

Steps to reproduce:

  1. Open the App Store app (or almost any app with a scrolling list).
  2. Scroll with a normal flick and let it decelerate.
  3. Observe repeated hitches during the scroll.

Measurements:
I filmed the screen with a second iPhone at 4K 120 fps and measured content movement frame by frame:

  • iPhone 18 Pro Max, third-party video feed: about 4 hitches per second of scrolling, about 4% of frames dropped, mostly single-frame drops.
  • iPhone 18 Pro Max, third-party social app list: about 11 hitches per second, about 12% of frames dropped, at a regular rhythm every 6-8 frames. About a third of the stalls last 2-3 frames, and the content does not catch up afterwards.
  • iPhone 17 Pro Max, third-party comment list: about 5 hitches per second, about 8% of frames dropped, including several full freezes of 50-75 ms.

Expected:
Smooth 120 Hz scrolling, as ProMotion is designed to deliver.

Is Apple aware of this issue? I am happy to provide videos, frame-by-frame data, or sysdiagnose logs.

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WilliamPhilips OP

Filed as FB25432914.
WilliamPhilips OP

Update: frame-by-frame measurements from 3 new recordings (Nov 5, 2026)

I filmed my iphone 17 pro max(iOS 27.2) with a second iPhone at 4K 120 fps and measured content movement frame by frame. Capture timing was verified (8.333 ms median frame interval, no gaps over 12 ms), so no camera frames were dropped.

A frame was counted as held when content stopped moving for a frame during active scrolling and then jumped forward to catch up. The alternating ~60 Hz cadence near the end of each deceleration was excluded, since it is likely ProMotion's intentional low-speed refresh rate reduction.

Results (hitch time ratio = held frames x 8.33 ms / seconds of active scrolling):

  1. App Store app, Apps tab
  • About 5.0 hitches per second, 6.7% of frames held
  • 13 multi-frame stalls of 25-33 ms
  • Hitch time ratio: ~67 ms/s
  • In several fast-scrolling segments, content updated only about 80 times per second instead of 120
  1. Third-party video app, feed list
  • About 4.2 hitches per second, 3.9% of frames held
  • Hitch time ratio: ~39 ms/s
  1. Third-party shopping app, search results
  • About 3.5 hitches per second, 3.6% of frames held
  • Hitch time ratio: ~36 ms/s

For reference, WWDC20 "Eliminate animation hitches with XCTest" describes under 5 ms/s as good, 5-10 ms/s as warning, and over 10 ms/s as critical. All three recordings are in the critical range, at roughly 3.5x to 6.7x the threshold.

Values are approximate, since the camera and display clocks are not synchronized. Original videos and frame-by-frame data are available on request.