So, after playing around a lot with the new bombs I noticed taking down large mobs took forever; and after looking closely, even though shards were hitting the enemy no damage was being done. You are even able to hear the shards hitting the enemy (creating the plink sound that happens when you attack gremlin or trojan shields). Took some video of the occurrence. It isn't rare that it happens- I can make it happen on command, and it's kind of annoying when a player wants to be doing as much damage as they can and end up doing none....
Can see what I mean here: Spiral Knights - New Shard Bomb Issues
I think it might have to do with invincibility frames.