Used to happen all the time when I used this monitor with a HDMI to VGA adapter on my laptop. I really don't know what was causing it, but it was so minor I just ignored it. It's on DVI now on my desktop and has no issues. Possibly bad connection as the HDMI port on my laptop wasn't too great, things had to be plugged in perfectly straight. Normally I would try the auto button, but it has none.
(Asus VW220, Windows 7 with the adapter, later Windows 10 with DVI)
My old desktop developed an issue where the monitor would say "AUTO CONFIG" like it always did when booting up, but instead of setting the screen correctly, it was way off by almost a centimetre. Simply pressing "AUTO" on the monitor fixed it. (However it was annoying)
(Acer AL1715, Windows XP)