Does snapping reset the plusses (e.g +4) in uno?
Chaning/Snapping/Stacking draw cards does not reset the penalty amount. E.G Player 1 plays draw 2, player 2 plays another draw 2, player 3, having no draw 2 cards, must draw 4 cards.

From wikipedia as a part of the house rules:


  Progressive Uno: If a draw card is played, and the following player
  has the same card, they can play that card and "stack" the penalty,
  which adds to the current penalty and passes it to the following
  player.