I've started to get this problem recently. I have a mirrorless Samsung NX1000. The problem is that my photos are overexposed, especially photos taken outside. I have to use an exposure compensation of -3 just to get decent usable photos. I'm getting overexposed photos in Aperture priority and Shutter priority even after setting the aperture to 20 and the shutter speed to 1/4000s. The overexposure is unusable. Here's an example:
EXIF Focal Length : 24mm F-Number : f22 Exposure time : 1/60 ISO : 200 Shutter Priority Exposure Compensation : 0
I'm not sure how this problem started. But about a year ago, my lens was broken due to a bumpy ride. Eventually, I was able to get it fixed in a camera shop. After the fix everything was working OK until now.