I am in exactly the same position.
I was a Lightroom standalone 5.7 user. I recently updated to CC. Photoshop CC works fine but I cannot update Lightroom or use Lightroom CC. I just keep getting the Lightroom 6 splash screen for a fraction of a second. No error messages whatsoever.
I have logged out of CC and logged back in again. I have also un-installed Lightroom CC and reinstalled it, still no joy.
Any help gratefully received..
Luckyleddy, found this
Adobe Lightroom CC 2015 is available. In some cases the program wil not start after installation. Only the start-up screen pops up and Lightroom will not start. If you have an Adobe CC (Creative Cloud) subscription you must do this: log out your CC account and log in again. Lightroom will now start as usual.
So I stay with my question:
Lightroom is not updating on my Mac. This lightroom version was installed solo, prior to my creative cloud subscription. In creative cloud i see updates for photoshop and creative cloud. Not for Lightroom. I did re-instal creative cloud.
According to Adobe it is not needed to re-install Lightroom when using creative cloud.
When checking in Lightroom it is mentioning the update and re-directing to Adobe site. There is mentioned that it is down loading. After this creative cloud opens and stays blocked with "Download error" no number mentioned.
thanks for some help.
After an update of the installer to version 9 everything works normal,
reply when you need more info.