Look at the magnetometer image on the left. There is some pretty obvious archaeology there, a couple of tracks and a small enclosure, but what are those large blobs? They must be archaeology too right? I certainly thought so, I even flagged them as archaeology in the report. Similarly with the image on the right, showing a track next to these features.
Actually, this is more annoying geology. This time, going under the name of Gley. Gley is often formed geologically adjacent to streams or other water courses. The example to the left is next to a stream, and the right next to the floodplain of a river. You don't want to dig that stuff up, very sticky.