You posted one image with no reference to what has changed.
LR works in the ProPhoto RGB color space and when exported it is more than likely being converted, and or save, to the sRGB color space. This change/conversion can have a slight affect on how the image appears.
But without seeing what you think has changed the image you posted looks fine. Other than is seems to be slightly washed out and has a haze to it. At least on my monitor in the Chrome web browser I use.