Metring

I own the Nikon Zf. I have the Urth lens adapter to use my manual Nikon F mount lenses with the newer body. I have been using the non-cpu setting for months. My camera is connected to wi-fi to allow for updates to the firmware. I know the exposure triangle and I have a manual light meter.

I have noticed that the in-camera light meter is failing me. Before I could set the light meter to 0 by using the meter on the screen to get a more accurate exposure but now I have to go far on the + side to even get an accurate exposure. At 0 I have a very underexposed picture. Can anyone explain what is going on inside the camera? Is it an update issue?