Are we talking about corners you need to brake and downshift for or just throttling off to slow down? Brake pads could need changing, fluids full in the master cylinders? Leaking anywhere?
You need to elaborate a bit. One thing I learned many years ago was to be a better rider that I needed to ride with people that are better riders than myself. Now I just need to slow my roll and take things at my own pace.
I had some cornering issues lately and couldn't figure it out until I checked the tires, low treads will obviously affect cornering. Low tire pressure can play games with handling as well.
Don't rule out the possibility of health problems also. Any kind of head cold can mess up your inner ear and therefore your balance. Might even be something you don't really notice, until you ride that is.