Description of the Issue: After multiple connect/disconnects the device will send pin/key missing at the final encryption steps.

Steps to reproduce:
1. Load a CC26X2 launchpad with Simple_peripheral software from the 6.10.00.29 SDK
2. Use a phone to connect, pair and bond to the CC26X2 device
3. Connect/Disconnect multiple times. After a while (occurrence once per day), you will see in some connection at the final step of encryption process, CC26x2 will send reject with reason code PIN or Key missing. The connection and disconnect duration is every 16 seconds.