The Canon 6D has been supported since LR 4.3 and PS-CS6/ACR 7.3 so you may need to update.
You can find LR updates on this page:
You should be able to update to ACR 8.7.1 via Help / Updates in PS’s menus.
Or if that doesn't work, you can download the ACR 8.7.1 installer from here:
Unless you’re still running an older OS, like Windows Vista or earlier or OS X 10.6.8 or earlier, then you’ll need the ACR 8.3 installer from here: