Read the report - there is
zero evidence of rape that hasn't been thoroughly debunked. That "reasonable grounds" line was apparently added to placate Israel by the report's author (who has a history with Israel).
Even the NYT now admits (albeit quietly) that their "expose" contains no evidence.
And, as I'm sure you know, there are exactly zero videos showing rape. Quite frankly, I find it incredible that some people still believe the atrocity propaganda, even when it's so obvious and of such poor quality.