Hello,
I bought a new bike frame with vertical dropouts and put my Alfine 11 on the rear. For chain tension I use a Surly Singleator and am experiencing chain skipping over the tensioner, which carries over to the cog and skips a tooth. This only happens with the singleator in push down mode and when I put more power through the pedals. In push up mode it's fine, probably because there is more chain wrap. I did put a new chain on the new bike and a new jockey wheel on the singleator, but haven't changed the cog or chainring there. The singleator was on my MTB in push down mode and never had this problem and I crank harder with a smaller chainring. I am okay with the tensioner in push up mode but like the look of the chain line in push down mode better. I suspect it's because the chainline is out by about 1mm between the chainring and the cog, but I don't think it's perfect on the MTB either.

I have no issues with 2 pulley spring loaded chain tension ers... essentially a short cage rear mech aligned to sit over the single cog,

I fit Tacx Pulleys on them.. so no real rolling Resistance.. to chain passing over them...







....

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