Yamaha YPG-525 Touch Response Out Of Whack

I own a YPG-525 keyboard. About three years after I bought it, the touch response on random keys started malfunctioning. As you know, when you normally strike a key based on your own touch response, that key will play soft or loud depending on hard you hit it. What happens with my keyboard is the touch response will randomly shut off for random keys, like for example, sometimes it happens to every E key where when you strike any E key on the keyboard, the touch response is off which produces a very loud and out of whack E key. Sometimes it happens to multiple keys but every other key that this doesn’t happen to works fine. What's weird is that it will do this for a few days and eventually, the problem goes away and all keys sound normal again. However eventually it will start malfunctioning again but it might be different keys that are malfunctioning. It's very random and extremely frustrating considering I use my keyboard in a band and can't use it when it does this. Is there any way this can be fixed? Any suggestions at all?

Thanks,
Tim