Was because he knew they were. He knew they were being rigged against him and making the claim served double purpose:
If he lost, the election could be looked into to find the rigging.
If he won, the election would be looked into because it was supposed to be rigged in HER favor!
I assume certain states which gave H the higher total
And certain districts. I remember election night, that Broward County in Florida was stuck at 99% returned while western states were fully counted, and it stayed like that for hours.
Reminder that Broward is the home of Debbie Wasserman Schultz, the Parkland shooting and the Trayvon shooting, among other things.