Was this present with 17.04 or any other 17.10 milestones?
This is the first time I have experienced it.
I always test pre-release isos when asked on lubuntu-devel on this particular netbook (Samsung NC10, 'hawking') so it is probably safe to say this is a new problem.
There is a graphics issue. I think the kernel parameters "splash quiet" somehow result in the graphics subsystem is somehow put into the wrong mode, resulting in the wrong piece of memory being used for part of the display, resulting in 80% of the screen being junk and 20% of the screen being perfect.
It appears that booting from being switched off completely, with the kernel parameters "quiet splash" removed, prevents the problem from happening in the first place.