Scratches in the build plate - How did this happen, and may it cause problems?
As the question continued in comments, it can be read that the build plate had over-tight screws and loose screws on the build plate. This uneven tension could lead to stresses that warp the bed, e.g. lower corner and bulging out in the middle of the bed. When levelling on the corners, the nozzle could hit the bulge in the middle when printing. Furthermore, an endstop may have shifted during operation.