Using Libre Office 5 - problems with large document

I have a document of 2000 pages - this opens fine in Libre Office 5 under Ubuntu 15.10 - but when I upgrade to Ubuntu 16.04 or 16.04.1 Trying to open the document results in a greyed out screen for at least 20 mins and then a hang of the system. Is the problem in Libre or Ubuntu - Has anyone else had the same thing

2000 pages? with images? the file is Mb Kb? and the memory (RAM) of the PC?

Maybe your user profile has become corrupted in the upgrade process. See if resetting it helps.

Reset user profile - no change