Sounds like a *[gremlin][1]*

>An imaginary mischievous sprite regarded as responsible for an unexplained problem or fault, especially a mechanical or electronic one:
*a gremlin in my computer omitted a line*

*Oxford Dictionaries Online*

For a longer discussion, see this article in *[Wikipedia][2]*


  [1]: http://www.oxforddictionaries.com/us/definition/american_english/gremlin
  [2]: https://en.wikipedia.org/wiki/Gremlin