This is most likely the culprit, especially being that the problem happens at the same spot in the crank rotation. There is no way that the random number of chain links (including the supposed bad one) lines up every time with the chainring/cog numbers. So...your chainring is not mounted properly and/or your chain is too tight when you mount the wheel. There should be some slack in the chain to account for this very situation. Generally, about 3/4" - 1" of vertical play is optimal. Yes, a chain can be too tight even if your chainring is perfectly centered. Friction of the chain within itself will create significant drag.