libreoffice crashing fvwm (or X11 ?)

Since a couple of months or so I moved my production environment to Opensuse leap 42.3, with bundled fvwm 2.6.6, and also bundled libreoffice (which replaces openoffice I was using on older OS) . In a couple of times I got a “crash” while I was editing a document (a different one each time).
Suddenly keyboard and mouse were not responding, and shortly touching any key logged me off the X11 session (not all child process were correctly killed though).

Could it be an fvwm or X11 problem ?
Anybody else experimented something similar ?