The most likely explanation is metering mode and how the camera evaluates the scene, not that both bodies are faulty.

Your D7100’s meter does not judge exposure from shutter speed and aperture alone—it measures the actual light in the scene. So 1/13s at f/4 could be perfectly normal in a dim environment, and a 0 reading simply means the camera thinks those settings match the scene brightness.

Also, if you’re using matrix/evaluative-style metering, dark edges or lens vignetting can influence the reading. The camera may average brighter and darker areas and still report 0 even if part of the frame looks like it should be brighter.

Things to check:

• Verify the metering mode (matrix, center-weighted, or spot).
• Compare readings on a uniformly lit subject.
• Check the histogram and highlight clipping rather than relying only on the meter scale.
• Be aware that lens vignetting or a high-contrast scene can affect the meter’s interpretation.

Since both cameras behave similarly, this points more to scene/metering behavior than a defect.