Fewer woumbgrafts when leveling

I've run a few test runs before the patch and any time I succeeded in a breach event I would get a woumbgraft. Since the patch I've only run once but when I complete a breach event in the low level areas sometimes I don't drop any woumbgrafts. I'm only talking about successfully completing the breach waves events in act1 and 2.

Is this new or was I just getting lucky before and unlucky now?