Can you tell me for how long the plant is inside that terrarium? Are u sure that there were no drastic changes on the environment recently? Nepenthes never go dormant. If the plant is disturbed while the pitchers are growing they stop doing it and stay closed.

i moved it outside to get a little sunlight and the temperature was about 15degrees lower than inside.

Couple questions. First, what kind of light does it get in the terrarium. Secondly, tell me more about the nep. Do you know what kind it is? How big is it? How long have you had it... did it ever have any pitchers that fully matured?

Going on just what you've said so far, I'd say you shocked it a bit with the move to outside and that caused it not to fully develope the pitchers. In which case, when the plant gets back to normal, it'll make more leaves which will make more pitchers. There are however, other possible reasons. Tell me more about your set up and the environment the plant is in.

Here is a link that might be useful: Tangled Web of Aracknight