That’s interesting tbh, especially given the one line in the middle. I usually use Cura, so I’m unfamiliar with the Prusa Slicer, what setting causes that variable speed?
But it’s fascinating, I can even see the bulge in the layer of the single line in your photo, now that I know what to look for. That’d also tell me that maybe you’re running it a bit hotter than it needs for this specific filament, maybe go down 5°C or 10°C. It seems when it slows down, more can ooze than it intends to.