Nightfall has already been reported to have less than expected uptime and procs per minute based on extensive raid logs.
I checked myself how many Nightfall procs I get when using wingclip in the same batch as my auto attack versus just auto attacking. I did this using the DMT spirits and Details.
With only auto attacks:
344 batches, 344 autos, 50 Nightfall procs.
14.535% chance to proc on hit. (Matches Blizzards reported proc rate)
With auto attacks batched with wingclip:
364 batches, 728 attacks, 42 Nightfall procs.
5.769% chance to proc on hit. (Well below Blizzards reported proc rate)
11.538% chance to proc per BATCH. (Matches Blizzards reported proc rate)
Based on these findings I would suggest that Nightfall only checks once per BATCH rather than per attack to see if it should proc. This would explain the discrepancy in Nightfall proc rate in logs versus Blizzards reported proc rate.
I know this is a relatively small sample size but when you consider the discrepancy in raid log proc rates too this is a clear indication that Nightfall is not working as intended and perhaps ALL proc weapons more generally are not working as intended.
We have seen multiple debuffs applied in the same batch tick, like this shaman proccing 2 nightfall debuffs off a windfury: https://cdn.discordapp.com/attachments/648260038372229134/679812474454671416/unknown.png