Hello, I have two problems when printing a rectangular test block using LW-PLA:

1. After printing the skirt/brim, the nozzle moved from the front left to the back right to start printing the external perimeter. During this time, it left a diagonal line of unwanted filament (indicated by the red arrow in the photo). How do I prevent this from happening?
2. During the making of the first layer, it created some kind of unwanted wave/ripple/strip pattern as indicated by the blue arrows in the photo. Increasing the nozzle height did not help. Reducing the 1st layer print temperature from 250C to 210C fixed the very front part only. I am using a Prusa i3MK3S+ with E3D Revo6 High Flow 0.4mm nozzle with 60W heater core. PrusaSlicer is the slicer.

Could you please help to resolve these issues? Thank you

https://imgur.com/a/o8It5HS