As an update, changing to a different brand of petg (polar filament) fixed it. I also changed to 230 nozzle and 70 bed, which is the recommended temp from the manufacturer for this new petg… the old transparent petg (from Kaaber) couldn’t handle these temperatures without liquefying and sucking on overhangs/bridges.

As many other stated, its nozzle ooze. When you travel the same path repeatedly, it will catch on previous ooze and build these diagonal structures.

Besides what other wrote, I can recommend:

• Try out how fast you can make your printer move, and travel as fast as possible. That gives your filament less time to ooze, and therefore you minimize the amount.
• When travelling, do a very small Z-hop. Something like .1mm. That helps a bit to not deposit the oozed material along the way, but where you touch down again. If you make the Z-hop too high, it will start to create strings. So you’ll have to try and tune this value.
• Generally try to slice in a way that minimizes travels. Even stuff like choosing an infill that doesn’t cross lines, and connecting those lines so that you print long and steady can help to keep your nozzle clean (I like gyroid with connected ends for that matter).
• What also helps is to convert your printer do direct drive. That gives more precise retractions. What works well for me is direct drive with small retractions. I believe, not shoving the filament back and forth so much yields better quality. Maybe, because retracting a large amount pulls air into the hot-end, and I imagine it might not all come out perfectly again when continuing with the next perimeter.