The first exception happens when an activity reports completion after it timed out or workflow already closed. If it happens frequently It usually indicates that activity timeout is too small.
The second exception is benign and should be changed to the DEBUG level. It means that a new event was received by the service while the workflow task tries to complete the workflow. To handle this race condition without data loss the workflow task completion fails and the task is retried. See this discussion that explains how this mechanism is used to ensure that signals are not lost in the presence of such race conditions.