We've seen this happen a few times with certain well-known and very-affordable brands of pre-ground coffee. After brewing, you might notice some of the grounds in the center of the filter still appear dry. If you use the kinds of beans mentioned above and notice this happening, here are a few fixes to try on your next batch (try them individually, in this order):1) Fill up water level to the tippy-top of the jar so it completely covers the cap. Coffee grounds float, so this ensures the grounds remain underwater while they steep. 2) Use a total of 4 "rumbles" rather than the recommended 2 rumbles ("rumbles" are the standard end-over-end horizontal rotations depicted in step 2 of our instructions).3) If those 2 additional rumbles still didn't do the trick to soak all the grounds, next time try giving it two horizontal shakes (i.e. hold the jar vertically, but shake the jar horizontally). This loosens up the grounds that might be caked onto the wall of the filter and plugging up the holes, which can prevent water from circulating. Don't overdo this step though...too much of it can create a lot of sediment.4) Consider using coarse grounds. They're recommended by the cold brew experts anyway, and we almost never see this dry grounds issue occur when brewing with coarse ones.