JPG artifacts after sharpening

Unlikely. If this was a Lightroom issue and not a user issue, then you would see complaints all over the place. This is not something that nobody else would notice... How do you view the exported jpegs?

You set the compression in the Export dialog. The Quality setting is the inverse of compression. The higher the quality the lower the compression. You can also limit the size of the exported image to a certain number of KB instead of using the Quality slider. That is a tricky one, because that means that the larger the exported image (in terms of megapixels), the higher the compression will have to be to accomplish that size. You could easily set a irrealistic number here.

Sounds like you may be using too much sharpening. Another possibility is too heavy compression when the jpegs are exported. Without examples it's difficult to say.