NimBLE reconnection fails when paired with Secure Connection enabled

[StevePeake]

Hello

I've just started using BLE in my project, using NimBLE (esp-idf v3.3.4).

I am using the bleprph example, with CONFIG_EXAMPLE_BONDING, CONFIG_EXAMPLE_MITM, and CONFIG_EXAMPLE_USE_SC all enabled.

I am connecting with an Android phone, using the LightBlue app.

I can connect, disconnect, and reconnect fine - so long as I don't write to the gatt_svr_chr_sec_test_static_uuid characteristic.

If I write to this characteristic, I have to accept a pairing request.

If I then disconnect, reconnecting fails.

After this failure, I can reconnect successfully.

I've seen exactly the same behaviour with the nRF Connect app. Using Bluetooth LE Explorer from my Win10 desktop has similar issues - trying to reconnect once paired causes a repeated stream of disconnections.

If I disable CONFIG_EXAMPLE_USE_SC, I can reconnect without being disconnected.

Logs from LightBlue app and bleprph output:

LightBlue_log.txt

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bleprph_log.txt

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Any suggestions how to investigate further would be appreciated.