This has occurred a couple of times since updating to the 2015 CC version through the CC panel. I will be in my workflow, keywording and captioning, developing once in a while and after a hour or so, LR will stop responding in a timely manner. I.e., I will be typing in a caption box and my keystrokes will get five, ten or twenty strokes before I notice they are not showing up anymore. I wait, and eventually they show up. Every change from one photo to another entails a minute or two of "working" messages, and when those finally clear, typing into title or caption or keyword boxes results in waiting a long time for each keystroke to show.
When I turn on the task manager and watch the processes, LR at this point varies from 17 to 20 % CPU, with another 1% being added from Chrome, Evernote or the task manager itself. RAM usage is around 30% of the 24 GB available.
I thought I saw somewhere in these forums something about a .01 update, but it is not showing up in the CC desktop.
When I try to quite LR by clicking the red X, I get a message that it is busy writing XMP data, but no worries, it'll finish next time I start it. So I tell it to quite. It doesn't, it continues to grab 17-20% of CPU until I kill it. I've waited 15 minutes.
When I start back up, it takes me to the place where I was the previous time I quit, rather than where I was when I killed it. As far as I can tell, all the edits I'd made have taken.
Probably related, sometimes instead of locking up, what will happen is that the keywords being displayed are completely wrong. Usually, if I switch to another folder they are good in that folder, though sometimes after a long period while the "working" message displays. When I return to where I wanted to be editing, usually I'm back to the keywords I was working with. If I'm not, a restart of LR tends to fix it. However, that is not really acceptable, since there is no message or warning that the keywords I'm looking at are not really the ones tied to the currently selected photos.
Also possibly related, when I recently imported 4 videos, I got a message telling my data drive (G) was dangerously low on space and telling me to go out and free up at least 20MB. The drive in question has 2.1 TB free!