Thats life my man.... thats the reason
Check your sproket to start with, usually a cheap sproket is not even at all... other reason could be that on of the cranck spider arms is out aliggment for 1mm for example... other reason could be the chain. Chains not always are ok.
To tell you the truth I havent seen in my life a track bike w/o a problem like the one u mention. ALways the chain tensions a little bit more in one side than the other one. Well if someguy uses non -expensive parts the problem is a lot more noticeable anyways.
I even have a BB tap to check the thread in the sprokets, the reason for that is that not always the thread in the sprokets are ok, so to avoid screw up the thread in the hub the best way to do it re -tap the theads in the sproket. After thant it will fit as a globe.
Another way to do this is to use an old and super used steel hub... put the cog there untill it turns like it had butter (use grease obviously) in it... after that put the cog in your real wheel. No problems at all... tips to make the hubs threads last a lot longer...