laravel query builder returns 0 record count but can iterate the results

I have this simple query that groups email address. I noticed that when i use whereDate, it always returns 0 count when i use $users->count(). however, when i remove the date where clause, it returns the expected result. Can someone help me on this? thanks in advance!

    $users = Wfa::where('subscribe', 1)
                ->where('locale', $locale)
                ->whereDate($whichDateColumn, '=', $queryDate->format('Y-m-d'))
                ->groupBy('email')
                ->orderBy('id', 'asc')
                ->get();

I'm using laravel 5.0.35; upgrading is not an option :(

via Chebli Mohamed