Nicehash Downtimes and Rejected shares

Hello, Im new to mining and I have setup nicehash on hiveos using Ethash. I have 2 questions:

  1. The rejected shares: I have a considerable amount to rejected shares; I read a post where it was suggested that Nicehash will always have rejected shares between 1-2%. I s this still the case and how does this affect profit in general (I assume a 2% loss).

  2. Down times: The graph on hiveos UI suggests a frequent down time of the service (as shown on the image attached). I notice nicehash regenerates DAG quite often whcih Im yet to understand why (still reading and researching things), Could this be the down time depicted on the graph. Sometimes the downtime ranges from 5- 20 minutes.

Is there something I can do to prevent these from happening.