Daytime image is good but the nighttime image is blurry or out of focus.
This is normally caused by the IRs reflecting back into the camera
First inspect the lens cover for dirt, debris, scratches, finger smudges or residue left over from a cleaning solvent.
Recommend cleaning with a dry micro fiber cloth.
Make sure the rubber gasket is properly seated on the lens.
Make sure the lens doesn't exceed the camera's recommended tilt. Check the user manual for specs.
Make sure there are no reflective objects too close to the IRs.