This has happened in all conditions. I would cast, sink the line then gradually the float would either sink (fished hard on the bottom) or start moving toward me (fished up in the water). When I lifted the rod there appeared to be a huge bow in the line going downward toward the lake bed. That's when I started to realise the stuff was sinking like a stone. I tried not sinking the line after casting when there was no wind but that did not make any difference it would just start to sink on its own. Very frustrating!
