Connection security failed: role: Central in ble_app_rscs_c


I am working on nRF52840 DK with nRF5_SDK_15.2.0_9412b96 and I used the example ble_app_rscs_c with absolutely no changes. I first erased the flash and then burned the Softdevice and app to erase any bonding. I used LightBlue on my iPhone to advertise 0x1814 (BLE_UUID_RUNNING_SPEED_AND_CADENCE). The first time I received the pairing request on iPhone. Every time I restart the DK, I receive the following error several times (4 to 5 times):

<info> peer_manager_handler: Connection security failed: role: Central, conn_handle: 0x0, procedure: Encryption, error: 4352

and then

<info> peer_manager_handler: Connection secured: role: Central, conn_handle: 0, procedure: Encryption.

Although it finally works, these failures cause a long delay.  I have also seen this problem reported for BLE peripheral examples but their solution (un-pairing from iPhone) does not work for me. I need to keep the devices paired.

I was wondering how I can fix this.