Water is still cool, so they are more picky. They are feeling the resistance of the bobber and spitting it back out.
Ditch the bobber.
I very rarely fish with one. I've fished SS with a bobber, but the bobber was just there to add more weight to be able to cast further. The hooks that I use are small enough and light enough so the SS floats. If when you cast, watch the bobber. Right before it hits the water stop the line coming off of your spool. The bobber will stop, the SS/hook will continue to go, and if you do it right it'll land as far from the bobber as the line will let it. If you don't stop the line right before it hits the water, the ss and bobber hit the water in the same spot.