Reworked a bit more in https://www.openstreetmap.org/changeset/134238394. Looking at the older OS mapping (OS 25 Inch 1892-1914) and the newer OpenData StreetView, it looks a lot like Escow Beck is culverted below the two footpaths/tracks before re-emerging and going into the Lune.

It can’t be a sinkhole here because the underlying geology is not limestone.