As described in the title. I just upgraded to Lightroom 5.0 and i have this weird problem. The exported image image results having a lot of Luminance and color noise when i use the resize module for exporting. If I export at full res there is no problem at all.
The setting that is giving me the problem is 1600px for the longer edge. If i select 3000px the image is exported correctly
Here you can see an example of a section of a photo comparing the problematic export with the correct one