auto tone suddenly overexposes

I have been using Lightroom Classic to process object photographs for a few years.  These photos are taken with the object in a lightbox against a neutral grey background with a color target.  The white balance is adjusted using the the dropper and a white on the color scale.  After adjusting the white balance, I normally just press Auto Tone and everything turns out looking good.  

However, in the past 2 weeks, suddenly all the photos are turning out overexposed.  I have not changed any camera settings nor Lightroom settings.

Can anyone think of a way to resolve this?