There is a slicer option that covers this problem up in many cases. It will not work in every case and it will not fix the underlying issue, but in this case it would have fixed it: Avoid crossing Perimeters.

You get these artifacts from filament dripping from your nozzle when the nozzle is traveling over empty area. The option above avoids traveling over empty space if possible.

You may be running the nozzle too hot for this filament. Trying lowering your temps more and see if that changes anything. Usually when my temps are high, that’s the first thing I see

I would try with another slicer to be safe. I trust you have cleaned your nozzle too?

This is basically just nozzle ooze. those little bumps are the extra plastic that’s come out when the nozzle is traveling.

I’m not familiar with prusaslicer, but in Cura there are settings called combing that help prevent the nozzle from traveling over plain air (thus the ooze gets left in the walls or infill), that might help, but honestly I’ve had this same problem and I’d love to hear if you find a good solution for it.

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.

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.