Send 20 bytes, client gets 15 bytes, when using PIN security for BLE connection

[Dave]

We have used nus profile for over a year, and it has worked as expected. Now we added security to the BLE connection, with ble sec connection enabled, it works as expected on Android.

However on iOS, the nus_evt handler just getting up to 15bytes even 20 bytes are sent.

what causes this, and how to fix it?

[Kenneth]

Hi,

To find out for sure I think we need a sniffer trace:
https://www.nordicsemi.com/Software-and-tools/Development-Tools/nRF-Sniffer-for-Bluetooth-LE 
https://infocenter.nordicsemi.com/pdf/nRF_Sniffer_BLE_UG_v3.2.pdf 

If I were to guess, I think it may be related to newline character:
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/ble_sdk_app_nus_eval.html#uart_data_handling

Best regards,
Kenneth