Error with super accessors

[liufengyun]

Compiler version

master and 3.1.3

Minimized code

abstract class A:
  val n: Int
  def foo(): Int = n

trait B:
  val m: Int
  def foo(): Int = m

trait M extends A with B:
  val a: Int
  override def foo(): Int = a + super.foo()

trait N extends A with B:
  val b: Int
  override def foo(): Int = b * super.foo()

  class Inner:
    N.super[A].foo()
    N.super.foo()

class C extends A with M with N:
  new Inner()
  val a = 10 // error
  val b = 20 // error
  val m = 30 // error
  val n = 40

Output

-- Error: examples/super.scala:21:6 --------------------------------------------
21 |class C extends A with M with N:
   |      ^
   |Member method foo$A of mixin trait N is missing a concrete super implementation in class C.

Expectation

It should compile without errors as in Scala 2.