Man I hate that thing... on my fourth run or so today I ran into a room full of like 4 or more of those things. Also, I went to verify what you said and somehow almost got roped into doing a whole run...
On topic though, They have a
Z symbol on them. There definitely isn't an element like that. (yet?) At first when I saw them my first thought was - "That's not an element... Could it be someone's name?" Almost like "somebody" has created the pucks. Or, it may also correspond to some sort of anti-elemental section. Kind of like the Harlequin who uses contraptions - some sort of machinery that we may encounter more types of.
edit: Also, anybody know how to counter them? I know how to attempt to avoid them running rampant, but is there a way to slow them down and make them stop moving? I tried to use the shield and back them into a corner, but they have too much knockback for me to get close enough for them to stop.