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I had a similar problem but not at such a small scale. It turned out there was a tiny thread of filament under my build plate, which caused uneven extrusion around that area. So now I carefully wipe off the heat bed every time I remove and reinstall the build plate.

It also looks like your first layer is pulling away from the build plate during the print. Are you using the powder-coated steel sheet? If so, I have found that alcohol doesn't help. Wash it in warm soapy water, rinse it, and dry in thoroughly while touching only the edges, and you'll get better adhesion. There are residual sugar compounds left over from the manufacturing process that alcohol doesn't remove, and they seem to leech out over time. I had to wash my steel sheet about every half-dozen prints over the course of a year before the sheet got "seasoned" to the point where alcohol is all I need now.