These EXIF fields can refer to different things.

• Shutter Speed may be the camera’s selected or reported setting, while Exposure Time can be the actual measured exposure. Those can differ slightly because cameras often use rounded display values, but the true timing may be a nearby exact value.
• Lens Aperture can describe the lens’s maximum aperture (for example, an f/1-capable lens), while F-Number is the aperture actually used for the shot (such as f/2.8).

So a file can legitimately show a lens capable of f/1 but shot at f/2.8, and a nominal shutter setting like 1/16 s with an actual exposure closer to 1/11 s. EXIF often stores both user-facing rounded values and more exact underlying values, which is why they do not always match exactly.