Survivors NOT making noise when being picked up

This has happened for me, and various streamers I have watched, it seems to be a universal bug.

It happens randomly, including within a same match. Sometimes, when the killer is picking up a downed survivor, the survivor does not produce the picking up grunt. The grunt is helpful for timing flashbang, especially against killers with unique pick-up animations, like the Onryo. The random occurence of no pick-up grunt makes this harder.