Xserver hangs randomly on Lubuntu 16.04 with Driver 340.98 (GT 220)

I am using GeForce GT 220 on 64bit Linux Lubuntu 16.04.
The “hang” is not reproducible, it happens following no visible pattern. It has happened more then once.
When this hang happens i can still move the pointer, but it does not change its lock when e.g. hovering over buttons. Everything else is not responding/working and i have to use SysRQ to reboot the computer.

I think this is a nvidia driver problem because the Xorg.0.log.old spams something about Nvidia and in the journalctl log there is one line about a gpu driver problem.
I hope this is the right place to report such issues.

i don’t get how to append a log file so i uploaded mine to dropbox: http://dl.dropbox.com/s/z2fyss4lv89ef04/nvlog.tar.gz
i added Xorg.0.log.old because this is the file in which the error is logged and because this file was not added to the generated log (i think).

little addition: Sometimes the same thing happens, but after some time the Xserver gets back to normal and i don’t have to forcefully reboot.
the error messages are nearly the same, but after one

[mi] Increasing EQ size to 1024 to prevent dropped events.
[mi] EQ processing has resumed after 1041 dropped events.
[mi] This may be caused by a misbehaving driver monopolizing the server's resources.

the (EE) errors do not start again.