Guys, even at v2.19, this problem hasn't been fixed. The Wipe Free Space feature has issues:
Case 1: When I wipe C:\ (system disk) alone, it completes the task.
Case 2: When I wipe C:\ along with other partitions/external storage devices, it hangs at 100% and won't jump to the next partition.
Case 3: When I wipe D:\ (non-system disk) alone , it hangs at 100.
Case 4: When I wipe D:\ along with other partitions/external storage devices, it hangs at 100% and won't jump to the next partition.
So basically, it only works when wiping the system disk. I really hope Piriform addresses this issue in the future versions.