BLE OTA Firmware Update fails on iOS 26.x — disconnects immediately when OTA begins #28
Description
BLE OTA Firmware Update fails on iOS 26.x — disconnects immediately when OTA begins
Summary
OTA firmware update via BLE consistently fails on iOS 26.x. The device connects successfully, but disconnects immediately when the OTA process starts. This issue occurs in both Reliability and Speed modes. The same device, firmware, and setup work perfectly on iOS 18.x and Android.
Environment
| Item | Details |
|---|---|
| iOS Version | 26.3 |
| iPhone Model | iPhone 13 Pro Max |
| Simplicity Connect Version | Latest (App Store) |
| BLE Chip | Silicon Labs EFR32 series |
| OTA File Format | .gbl |
Additional Observations
- Both Reliability and Speed modes fail with the same behavior (immediate disconnection)
- The BLE connection itself is established successfully — the issue only occurs when OTA data transfer begins
- The same firmware file and same hardware device work correctly on iOS 18.x and Android, confirming this is not a firmware or hardware issue
- A custom app using the same OTA process also fails identically on iOS 26.x, confirming the issue is not specific to Simplicity Connect
- This behavior is consistent with widespread BLE connectivity issues reported on iOS 26.x across the Apple Developer Forums, including:
- BLE Connection Drops on iPhone 17 — PHY switching causes disconnections
- iOS 26 Bluetooth disconnect issues — continuous disconnect/reconnect loop
- Bluetooth connectivity issues after iOS 26.1 — widespread BLE failures
Possible Root Cause
iOS 26.x appears to have introduced changes to CoreBluetooth's connection parameter handling and PHY management. During OTA, the large data transfer likely triggers a PHY switch or connection parameter renegotiation that iOS 26 handles incorrectly, causing an immediate disconnection. This has been partially acknowledged by Apple in iOS 26.2 beta for PHY switching issues, but the problem persists in iOS 26.3.
Workaround
Currently, the only workaround is to perform OTA firmware updates using:
- An Android device, or
- An iOS device running iOS 18.x or earlier
Request
- Could Silicon Labs investigate compatibility with iOS 26.x CoreBluetooth changes?
- Are there any known workarounds or configuration changes (e.g., connection parameters, MTU size, PHY preferences) that could mitigate this issue?
- Has Silicon Labs filed a Feedback Assistant report with Apple regarding this regression?
Related Issues
- Apple Developer Forums: Core Bluetooth tag — multiple reports of BLE issues on iOS 26
- Apple Community: Bluetooth issues with iOS 26.2
Summary
OTA firmware update via BLE consistently fails on iOS 26.x. The device connects successfully, but disconnects immediately when the OTA process starts. This issue occurs in both Reliability and Speed modes. The same device, firmware, and setup work perfectly on iOS 18.x and Android.
Environment
| Item | Details |
|---|---|
| iOS Version | 26.3 |
| iPhone Model | iPhone 13 Pro Max |
| Simplicity Connect Version | Latest (App Store) |
| BLE Chip | Silicon Labs EFR32 series |
| OTA File Format | .gbl |
Steps to Reproduce
- Open Simplicity Connect app on iPhone running iOS 26.3
- Scan and connect to the Silicon Labs BLE device
- Navigate to OTA Firmware Update
- Select the
.gblfirmware file - Choose either Reliability or Speed mode
- Tap Upload to start OTA
Expected: OTA firmware transfer begins and completes successfully.
Actual: The BLE connection drops immediately when OTA transfer starts. The device disconnects and OTA fails.
Test Matrix
| Platform | OS Version | OTA Result |
|---|---|---|
| iPhone 13 Pro Max | iOS 26.3 | ❌ FAIL — disconnects when OTA starts |
| iPhone (older) | iOS 18.x | ✅ PASS — OTA completes successfully |
| Android device | Latest | ✅ PASS — OTA completes successfully |
Additional Observations
- Both Reliability and Speed modes fail with the same behavior (immediate disconnection)
- The BLE connection itself is established successfully — the issue only occurs when OTA data transfer begins
- The same firmware file and same hardware device work correctly on iOS 18.x and Android, confirming this is not a firmware or hardware issue
- A custom app using the same OTA process also fails identically on iOS 26.x, confirming the issue is not specific to Simplicity Connect
- This behavior is consistent with widespread BLE connectivity issues reported on iOS 26.x across the Apple Developer Forums, including:
- [BLE Connection Drops on iPhone 17](https://developer.apple.com/forums/thread/806970) — PHY switching causes disconnections
- [iOS 26 Bluetooth disconnect issues](https://discussions.apple.com/thread/256164973) — continuous disconnect/reconnect loop
- [Bluetooth connectivity issues after iOS 26.1](https://discussions.apple.com/thread/256180011) — widespread BLE failures
Possible Root Cause
iOS 26.x appears to have introduced changes to CoreBluetooth's connection parameter handling and PHY management. During OTA, the large data transfer likely triggers a PHY switch or connection parameter renegotiation that iOS 26 handles incorrectly, causing an immediate disconnection. This has been partially acknowledged by Apple in iOS 26.2 beta for PHY switching issues, but the problem persists in iOS 26.3.
Workaround
Currently, the only workaround is to perform OTA firmware updates using:
- An Android device, or
- An iOS device running iOS 18.x or earlier
Request
- Could Silicon Labs investigate compatibility with iOS 26.x CoreBluetooth changes?
- Are there any known workarounds or configuration changes (e.g., connection parameters, MTU size, PHY preferences) that could mitigate this issue?
- Has Silicon Labs filed a Feedback Assistant report with Apple regarding this regression?
Related Issues
- Apple Developer Forums: [Core Bluetooth tag](https://developer.apple.com/forums/tags/core-bluetooth) — multiple reports of BLE issues on iOS 26
- Apple Community: [Bluetooth issues with iOS 26.2](https://discussions.apple.com/thread/256217277)