I recently run into the same problem.
The only solution I found was to restart the bluetooth (turn bluetooth off and turn it back on).
In my case, it was a change in the bluetooth device (restarting it in DFU mode) that always caused this problem, so I ended up showing an alert to the user to restart the bluetooth. Listened for centralManagerDidUpdateState:‘s Powered Off and than Powered back On state event to determine if the restart was done.