Gimp 2.10.14 histogram

[rich2005]

It looks like a bug to me. Might start with 0 - 255 but as you report, as soon as an image is opened then goes to 0 to -0 Depending on precision should be 0 to 255 or 0.000 to 1.000

I could see nothing to force a 'saved' 0 to 255

I had a search but nothing reported yet.
You should bug report here: https://gitlab.gnome.org/GNOME/gimp/issues/