It looks like this:
https://imgur.com/a/Om45uNg
There is a horizontal line, 1-pixel in height, that remains static within the EQ window. Anything this line touches is effectively removed, i.e. a 1-pixel height line is removed from visibility. This is mostly noticeable in text, effectively squashing the adjacent rows together. There are many of these "lines" on the screen, seemingly spaced evenly across the EQ window.
In the first image linked, you can see this line is cutting off the last row of pixels in the MOTD. In the second image link, I have moved the actual UI window in game a little bit so the same line is now striking through the center of the MOTD.
I assume it is somehow resolution related. I play on a laptop with an external monitor. On the laptop screen at 1920x1080 native and matching resolution EQ window, I do not get these lines. On external monitor at 2560x1440 native and matching resolution EQ window, these lines are present.