This looks as though the send_response_result member of ProtobufResponder is no longer valid (i.e. that the ProtobufResponder at this=0xac900574 has likely been freed).
I'm not sure what sequence of events would lead to a send_response() message being passed to a no-longer valid ProtobufResponder - but is likely to be a race within Mir between closing the connection and the compositor::BufferQueue::give_buffer_to_client() sending a buffer to the client.
This looks as though the send_response_ result member of ProtobufResponder is no longer valid (i.e. that the ProtobufResponder at this=0xac900574 has likely been freed).
I'm not sure what sequence of events would lead to a send_response() message being passed to a no-longer valid ProtobufResponder - but is likely to be a race within Mir between closing the connection and the compositor: :BufferQueue: :give_buffer_ to_client( ) sending a buffer to the client.
I'll audit the Mir code in this area.