Print issue
I haven't seen an issue like this before. I am relatively new to 3D printing so have only gone through a couple kg of prints... What might the discoloration be from? Looks like the outer layers were pushed out at the discoloration.
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RE:
It looks like a "blob" that accumulated on the nozzle and discolored from long heat exposure, then grew large enough to get snagged / deposited on that perimeter.
Two common causes of that are over-extrusion and stringing. If over-extrusion, dropping the extrusion multiplier a few percent may solve it. There are lots of reasons and solutions for stringing, but one of the biggest is damp filament (especially with PETG). As a first step, thoroughly dry the filament -- even if it is a brand-new roll right out of the package.