Updated: Having triggered the Synology update as of today 6th May 2017, the issue seems to have been resolved.
I think I'm suffering a memory leak issue with Lightroom. Today I've started getting memory warning issues from Windows and it wants to shutdown LR. The only thing I know of that's changed is that I ran the Excire Search plugin overnight to update the index. But that completed ok, and I've restarted the machine and replicated the problem without re-using Excire.
I do store my photos on a network drive - a Synology NAS drive. Ah. Thought. There was a Synology DS213 update a day or so ago, and there's another one overnight. I've installed that and am testing to see if that fixes this issue. YES IT DID
Lightroom version: CC 2015.10 [ 1111918 ]
License: Creative Cloud
Operating system: Windows 10
Application architecture: x64
System architecture: x64
Logical processor count: 8
Processor speed: 3.4 GHz
Built-in memory: 8144.3 MB
Real memory available to Lightroom: 8144.3 MB
Real memory used by Lightroom: 645.9 MB (7.9%)
Virtual memory used by Lightroom: 725.0 MB
GDI objects count: 421
USER objects count: 965
Process handles count: 1614
Memory cache size: 226.2MB / 1780.0MB (12.7%)
Maximum thread count used by Camera Raw: 8
Camera Raw SIMD optimization: SSE2,AVX
Camera Raw virtual memory: 52MB / 4072MB (1%)
System DPI setting: 96 DPI
Desktop composition enabled: Yes
Displays: 1) 1920x1080
I've had similar problem on my Mac recently with 2015.10. At one point LR was using 4GB of RAM. Mac OS also paused LR and asked me to free up some memory.
And then there are the more frequent crashes.