i got an email saying that LR cc no longer displays images of jpgs it created in its export process.
the problem is not from exporting images, the problem is when you import JPG from your camera memory cards, then you need to use auto tone to be able to see your images otherwise it's a black screen like showed by kenr18174589 , only RAW images are showing properly when importing images.
like i said, so far I reinstalled 6.0 and will not update to 6.2.1 until the next update.
another issue with 6.2.1 is after playing with LR for a while, the program crash/freeze and need to restart, the only way to close the program or close is to right click and force quit (on MAC).