I have imported a number of new images taken with a Canon 6D EOS. The images have been imported from an external drive and also directly from an SDcard. The import appears to process nicely, but when I chose the directory from the catalog all images are blank until I select "one" and then reset the values in the develop module. Once I've done that, the image appears in the catalog, but I have to do that image by image and it doesn't appear as though I can select a group.
For existing photos, select all your images in Grid view, and then click the Reset All button in the Quick Develop panel. Then click the Auto Tone button to properly apply this feature.
To prevent this from occuring in the future, choose Lightroom > Preferences > Presets (Mac OS) or Edit > Preferences > Presets (Windows). Uncheck Apply auto tone adjustments.
Hope it helps.