So I have a large Lightroom library (about 200K images) and recently changed to a larger SSD so I can have at least standard previews on all my images.
Initially I selected all photos in my library to start rendering previews - but it would stop after a few hundred and I'd have to cancel the task and start it again. I did smaller lots, but sometimes it still happens.
Is there a reason why this is? I'm not sure what photos it gets stuck on - I suspect it may be the JPEG and not the RAW files that it's stuck on, but I'm not entirely sure if that is the case.
I'm running Lightroom 5.6 on a Windows 8.1 x64 machine - hardware is up to the task, and the Lightroom previews are stored on a 512GB SSD with ample free space available.
This is still an ongoing issue with Lightroom CC 2015.8 (latest available at time of writing).