Why is this an issue?

Overriding methods automatically inherit the params behavior. To ease readability, this modifier should be explicitly used in the overriding method as well.

Noncompliant code example

class Base
{
  public virtual void Method(params int[] numbers)
  {
    ...
  }
}
class Derived : Base
{
  public override void Method(int[] numbers) // Noncompliant, the params is missing.
  {
    ...
  }
}

Compliant solution

class Base
{
  public virtual void Method(params int[] numbers)
  {
    ...
  }
}
class Derived : Base
{
  public override void Method(params int[] numbers)
  {
    ...
  }
}