Lr edits get "washed out" & pixelated when I export them.

Most of the time, (but not always), after I edit a photo & export it in Lr, it gets all "washed out" looking & pixelated. This never used to happen & only started about 2-3 weeks ago. I've been on the phone to Adobe customer service & shared my computer with them many times for hours on end, with no solutions. Is anybody else having this problem or does anybody have any solutions?