1) Since the cryopods have never failed, there's no need for back ups. THEY. HAVE. NEVER. FAILED. (Mission critical system)
2) Only one automatic doctor table for the entire crew of 5000 people (Mission critical system)
3) The ship is travelling autopilot engaged with nobody awake. (Mission critical system)
4) The said autopilot can be shut down without waking up the ship's crew. (Mission critical system)
5) The ship's diagnostic systems can fail without waking up the ship's crew. (Mission critical system)
6) The ship's fusion reactor control computer can get damaged and it can still spread its calculation load to other cores (good), but the said other cores have not been designed to handle the data flow. This makes the fusion reactor control computer a Mission critical system. If the data is loaded to other cores, the crew is once again not alerted.
7) The ship can lose its artifical gravity without causing an immediate crew wake up. (Mission critical system). Once the artificial gravity was lost caused one of the more creative scenes in the movie which includes a swimming pool. Nuff said. It's just that the gravity is lost almost immediately, and the habitation modules are quite large. Once the motors spinning the modules run out of power, the modules keep on spinning until friction takes away the stored rotational momentum. BUT: THAT. DOES. NOT. HAPPEN. IN. SECONDS.