1mm of chain line offness should not matter to a "single" chain/cog/ring system.. I also question that the tensioner pulley has anything to do with the skip too. Being spring loaded the pulley only has the spring's force acting on the chain. Now the amount of chain wrap around the cog, from the pulley pulling up or pushing down, very much can affect the chance of skip. I would look at the cog, compare to a new one for tooth profile/shape. I suspect you'll see tooth wear. I also suspect a new cog will clear things up. Ring teeth do also wear but with so many points of engagement, compared to the cog, it takes more wear to get ring skip. Andy