Yeah, it happens sometimes when OS/Video Card don't fully reconize your monitor. To fix this, go on google, write your monitor's model on it (somewhere around your screen, probably on one of the two top corner) + drivers. (e.g. LM220WE1 driver) than try to find one driver (I didn't try to find yours because first I didn't have your monitor's model and second : because LG's website doesn't help at all).
It happened to me like 1 year ago, I just downloaded the driver than I was able to put it to 85hz, but of course, I just wanted 60hz
and it helped too for a dual-screen configuration.
Hope it helps!
(P.S. the driver takes like 0.5 or 1 second to install, so don't think something went wrong)