unreliable

adj

1. Not reliable.

   “Tell one another whether any one of you has ever heard me discuss such questions briefly or at length; and then you will realize that the other popular reports about me are equally unreliable.”

   “The opposite issue emerges in the summer when students face scorching temperatures with unreliable or nonexistent air conditioning.”

   “"Operating the WCML at this intensity makes it challenging to maintain acceptable performance levels, resulting in a frustratingly unreliable service for passengers. Minor disruption can escalate into significant delays because a train running only a few minutes late can miss its slot across a junction, resulting in a snowballing effect across the network."”

noun

1. One who or that which cannot be relied upon.

   “His employment by the leading papers in Chicago was intermittent, as he was classed among the unreliables. One could never tell when he was going to get drunk.”