Layers not visible even though 'eye' is on and Hide layers isn't selected?

[frankg_photos]

I noticed a 16 bit Tif being unusually large in MB size and checked the Layers & Channnels but didnt see anything in them (except of course the one layer and 3 channels). I nevertheless Flattened the layers and voila the file shrunk to the expected size. Why would the layers (whatever they were?) have been hidden and how do I prevent that that.

Thanks