Please post a screenshot of the image and the export settings you have used.
A screenshot of the Detail panel (sharpening and noise reduction) in Develop could also be useful.
Is this a high ISO image? (select the original in Library, and see ISO speed rating under Metadata)
What was your export settings ?
Are you ok with sharing the image and the screenshot of the export settings.
Which version of Lightroom?
Have you changed anything on your machine?