While there are multiple instances of technological failure in Alien: Covenant, we would like to argue that none of them are due to a lack of reliability. First, both the ship's systems and the surface-to-orbit communications fail due to external factors, the former due to the neutrino burst disaster at the beginning of the movie, and the latter due to the planet's ionized exosphere. The topic of computer reliability mainly concerns failures caused by flaws in the technology itself and cases that designers may have overlooked, and these external factors that caused these failures are neither of those. However, whether David's genocidal tendencies are a result of his unreliability as a computer are less cut and dry. If you consider that David's purpose and the reason he was designed is to assist humanity, then obviously him committing murder and performing human experimentation is a technological failure caused by a design error. An argument could be made that the reason for Walter's lack of creativity and humanity compared to David is because a design change was made to counteract this flaw in David. However, if you consider David's purpose to be to replicate human thought process and emotion and come to his own conclusions, then perhaps he is working as intended throughout the movie.