BLE Connection Drops on iPhone 17 Series When 2M PHY Update Fails (Does Not Fallback to 1M PHY)

Hello Apple engineering team,

We are encountering a BLE connection issue on iPhone 17 series devices running iOS 26.x, while using CoreBluetooth to connect to our Bluetooth accessory in our app Aroma-Link. The problem does not occur on previous iPhone models or earlier iOS versions.

Issue Summary

Our BLE device uses a specific chipset batch where the 2M PHY capability is not fully supported. The expected behavior (as observed on iPhone 16 / 15 / older models) is:

Connection starts on 1M PHY

System attempts to upgrade to 2M PHY

If 2M PHY upgrade fails → system should fallback and continue using 1M PHY

Connection remains active

However, on iPhone 17 series:

After the system attempts to switch from 1M to 2M PHY and the upgrade fails

The device disconnects immediately

No fallback to the original 1M PHY occurs

This results in an unintended and user-visible disconnection.

Reproduction Steps

Use an iPhone 17 series device running iOS 26.x

Connect to the target BLE peripheral via CoreBluetooth (centralManager connectPeripheral)

The system Bluetooth stack initiates a PHY upgrade from 1M → 2M

The peripheral rejects / fails the PHY update

The connection is disconnected automatically

Observed Result

centralManager:didDisconnectPeripheral:error: is triggered immediately after the PHY update fails.

Expected Result

The connection should remain active on 1M PHY, consistent with behavior on:

iPhone 16 / 15 / 14 / etc.

Earlier iOS versions

Impact

This causes:

Connection instability specifically on iPhone 17 users

Inconsistent BLE behavior across device models

Unexpected disconnection despite valid 1M PHY link capability

Environment Item Details App Aroma-Link Bluetooth Framework CoreBluetooth Devices Affected iPhone 17 series iOS Versions iOS 26.x Reproducibility 100% BLE Peripheral Chipset Specific batch with known 2M PHY limitation Request

Could Apple confirm whether the PHY fallback behavior has changed on the iPhone 17 BLE stack, and whether this is an intended change or a regression?

We are happy to provide:

iOS sysdiagnose logs

HCI sniffer captures

Peripheral firmware logs

Please advise on the recommended next steps for debugging or mitigation.

Thank you.