This has been happening for years on many different computers / versions of Windows and versions of LibreOffice.

Currently running latest version of Windows 7 x64 SP1 with all current critical windows updates installed (but also had problems on numerous previous states of Windows)

Currently running LibreOffice Version: 5.1.2.2 (x64)
Build ID: d3bf12ecb743fc0d20e0be0c58ca359301eb705f
CPU Threads: 8; OS Version: Windows 6.1; UI Render: GL; 
Locale: en-US (en_US)

Open a new database, create a few tables with a few random record in them, save file, sit idle for a while or more easily, put the computer to sleep.  Wake up computer and LibreOffice window will be grey or black, clicking on it invokes the standard windows "Program Not Responding" response (in title bar and then with a dialog asking to close the program or wait)  LibreOffice never recovers, document recovery is invoked upon restarting LibreOffice after force closeing.

Similar to bugs:

https://bugs.documentfoundation.org/show_bug.cgi?id=35424
https://bugs.launchpad.net/df-libreoffice/+bug/745836
https://bugs.documentfoundation.org/show_bug.cgi?id=33025
https://bugs.documentfoundation.org/show_bug.cgi?id=40766

but not duplicates
because this is on the Windows operating system (these bugs are Linux / "other") and neither my "home" directory nor my "swap" paging file / virtual memory are or have ever been encrypted.  I verified this with run as admin cmd.exe by typing "fsutil behavior query encryptpagingfile" and got back response "EncryptPagingFile = 0"