Things I would check and try. (not in any particular order)
Check brake pads for wear thickness and or uneven wear.
Check General condition of disc.
Check for any air in the system, bleed brake.
Check moiture content of brake fluid, and replace if suspect. Your local dealer should be able to measure the moiture content and or replace if u not sure.
Check for a warped disc. this would cause the pads to knock back, hence a long pedal when you use it. Is there any indication of uneven braking or pulsing at the lever?