Most chainrings are not perfectly round. Some are worse then others.
For singlespeeders this can sometimes make achieving correct chain tension a trick. To do this you approximate the tension, then rotate the crank to find the “tight” spot, then set tension from that position.
However, this assumes you didn’t forget to center the chainring in the first place! I learned the hard way and didn’t think about it when I originally threw on the chainring (sort of a SS noob). The variance was too much, either it was too loose and bounced off, or too tight and would bind some with each revolution.
I dropped a chain again recently… finally got off my butt and took the time to better center the chain ring on the crank spider/mounts. Maybe its just Salsa rings, but the fit is quite loose and it took some trial and error to get it fairly center.
Good to go now though: