As far as what could be contributing to a difference, other than an actual bug:
LR Previews are stored as AdobeRGB JPGs, so Library previews go from LR-Internal color profile to AdobeRGB to Display color profile, whereas Develop previews go directly from LR-Internal color profile to Display color profile. If there are some colors that are outside of AdobeRGB then some conversion may occur. The conversion to 8-bit JPG is also probably adding banding that Develop wouldn’t show. There might also be Relative vs Perceptual color profile conversion differences occurring. I don’t know the specifics of which is used for the Adobe color profile conversion and whether what you’re seeing is outside the expected variations.
If you view at less than 1:1/100% zoom, especially with Fit or Fill, then small details that vary across the group of original image pixels that are displayed as one display pixel can be averaged differently due to differences in the downsampling algorithms used between computing Library file previews and computing Develop display previews where Develop’s is built for speed because it occurs in real-time after every slider movement, where Library previews are computed in the background and so can use a more accurate resampling algorithm. Usually this is only a difference in sharp/smoothness but it can also manifest as a difference in tone if there are lots of tiny noise spots getting averaged together and