Also happens on the jelly-pro:

All permissions are given.

08-31 23:39:16.615 9242-9318/org.briarproject.briar.beta.debug E/ACRA: ACRA caught a SecurityException for org.briarproject.briar.beta.debug
                                                                       java.lang.SecurityException: Permission Denial: Enable bluetooth requires com.mediatek.permission.CTA_ENABLE_BT
                                                                           at android.os.Parcel.readException(Parcel.java:1683)
                                                                           at android.os.Parcel.readException(Parcel.java:1636)
                                                                           at android.bluetooth.IBluetoothManager$Stub$Proxy.enable(IBluetoothManager.java:302)
                                                                           at android.bluetooth.BluetoothAdapter.enable(BluetoothAdapter.java:930)
                                                                           at org.briarproject.briar.android.keyagreement.ShowQrCodeFragment$1.run(ShowQrCodeFragment.java:166)
                                                                           at android.os.Handler.handleCallback(Handler.java:836)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:103)
                                                                           at android.os.Looper.loop(Looper.java:203)
                                                                           at org.briarproject.bramble.system.AndroidExecutorImpl$1.run(AndroidExecutorImpl.java:36)
                                                                           at java.lang.Thread.run(Thread.java:761)

You can prevent the crash by switching on Bluetooth.