Are you using any external disks? I had the same sort of hangs on el capitan that turned out to be caused by a USB connector that wasn't pushed in all the way. When Lightroom needed images from that it would lock up completely. Apart from that, I would make sure to clean out the ACR caches both for images and video (Preferences->File handling). If it locks up during purging your video cache it might be another bug for which there is a solution apparently.
I'll check the USB 2 ports now.
I'm also using Thunderbolt - same problem and a USB 3 - thunderbolt adaptor as my iMac is USB2 only.
It does not crash on my MBPro, but i'll try making a library on my internal hard drive and see what happens then.
I'll clean the caches again and see what happens there as well.
I don't use video, so that should not be an issue
It does not hang - rather just crash out and I often lose my last edit - I should have explained that more clearly in my question
So Lightroom just quits? It's not a complete hang of Lightroom and computer? That's probably not the disks then. This might be one of those very few times that a reinstall is in order.