I have the same problem as the OP, i did a gig on fiver for a customer, it was 1k scrapebox blast, he told me that my urls have N/A pr, i checked with scrapebox and most of them really have pr N/A, after that i checked them by hand and they had PR 6 and 7 cause i used this list before to and i know most of them have PR2-7, i checked this urls by several plugins in mozilla that i use forever now and i used some new ones, plus i have some softwares that i use and i tryed some online ones, most of them are showing the real PR, i compared with some authority sites so i make sure im not wrong.
There is something happening with scrapebox, but i am sure the developers are working on it already they are always make things right, its just a matter of time.