Hey there, sorry to hear you're stuck with this crash that only hits the iPhone 4s on iOS 9—super annoying when issues are isolated to old hardware/OS combos! Here are some targeted troubleshooting steps I’d run through:

• First, dig into the crash log (critical!)
  Grab the symbolicated crash log either via Xcode’s Organizer, or from the device itself (Settings > Privacy > Analytics & Improvements > Analytics Data). Focus on the crash type (is it EXC_BAD_ACCESS from a dangling pointer? EXC_RESOURCE_MEMORY from low memory?) and the call stack for Thread 0. Look for any references to your ad SDK’s methods or the code that triggers the ad display—this will narrow down whether the issue is in your integration or the SDK itself.

• Check for memory overload
  The iPhone 4s only has 1GB of RAM, and iOS 9’s memory management is stricter than newer versions. Use Xcode’s Memory Graph Debugger or Instruments’ Allocations tool while reproducing the issue on the device. Watch if memory spikes right before the ad is supposed to show—if the app is already near the memory limit, the system might kill it. Also, check if your ad SDK has any settings to reduce memory usage for low-end devices (like disabling preloading high-res videos).

• Verify ad SDK iOS 9 compatibility
  Double-check your ad SDK’s documentation to confirm it still supports iOS 9. Many newer SDK versions drop support for older OSes, so if you’ve updated the SDK recently, that could be the culprit. Try rolling back to the last SDK version explicitly listed as supporting iOS 9 and test again.

• Check video encoding compatibility
  The iPhone 4s doesn’t support HEVC (H.265) video encoding—if your ad videos use this format, iOS 9 on the 4s will fail to decode them, leading to crashes. Confirm the ad videos are using H.264 (which is supported across all iOS 9 devices). You can test this by embedding a sample H.264 video in a simple demo app and running it on the 4s to rule out hardware decoding issues.

• Audit iOS 9-specific API differences
  Your ad display code or the SDK might be using APIs that behave differently (or don’t exist) on iOS 9. For example, UIKit layout changes, AVFoundation playback logic, or even privacy permission handling. Look for calls to APIs marked as available in iOS 10+ in your integration code—if you’re using those without version checks, that could cause crashes.

• Test a minimal reproduction case
  Create a bare-bones demo app with just the ad SDK integration and the code to show the interstitial ad. Run this on the iPhone 4s—if it crashes, the issue is likely with the SDK or its basic integration. If it doesn’t, then the problem is tied to interactions with your app’s specific code (like conflicting view controllers, memory leaks, or state issues).

内容的提问来源于stack exchange，提问作者faris97