That's the extra materials. Jumping from 1 to the occasional 2.I think the system is actually broken-broken. The grimoire card for Mars/Meridian Bay says that once you rank up, "Extra materials drop from material nodes in this destination". I haven't noticed a bit of difference before and after I completed all three ranks for this card. I still get one or two materials per node. Having spent 29 hours (8000 kills) killing shit at this location should have me popping 5's and 10's. I really think they meant for these cards to do stuff, but they didn't get to it or it's broken.
Every now and then a random chest with 8-10 in it.