The filament is almost impossible to remove Most people complain about the filament not sticking on build plate but mine is vice versa. At first it used to be very good. When I removed the magnetic bed the project would come off easily but for a few days it is like I glue it to the bed with epoxy. It is impossible to remove and when I remove the black projects from the bed I see white color at the bottom of the object printed. Maybe because of too much force but I don't know why this happens.
This usually happens when your nozzle is too close to bed during the first layer.
  Quick fix is redo bed levelling.
  Clean your build surface.
Watch you first layer