This is the first in a series of troubleshooting 3D printing problems – mostly my notes on what has worked for me.
This was occurring because I was printing too fast, not giving the filament on the previous layer time to cool before placing the next layer on top.
In my slicer, PrusaSlicer, I changed Filament Settings -> Cooling -> Cooling Thresholds -> Slow down if layer print time is below to 15 seconds – this ensures that each layer takes a minimum of 15 seconds to complete. The result was a near-perfect benchy.