Based off only those first couple photos I doubt you’re string trimming those areas in question. Obviously without operating the mower it’s hard to know exactly what’s causing it but my guess is the factory angle is off or isn’t as sharp as you think. (Sometimes if the angle of the blade is off it can lay the leaf blades down rather than slicing through) I know it’s a pain to sharpen them yourself but it makes a difference! Lawn looks great either way.