The warranty is on the card this came with and not at https://www.asus.com/us/Monitors/MG248Q/HelpDesk_Warranty/ but once you figure out if it's in warranty use this link to contact Asus.
Your description gives me the idea it's a failing chip, connection or solder joint. It does not tell us much more than this. These are rarely repaired OOW (out of warranty) due to service costs, shipping, etc.
I've had this monitor for about a year now and the problem I am about to show you has happened around 4 times since I got the monitor. The first time it ever happened was about 5 months into using it. What happens is out of nowhere a red vertical line will appear on the right side of my monitor.
Here is a picture of what it looks like: http://prntscr.com/mwykfv
Here is what monitor I have: https://www.amazon.com/gp/product/B01F9UC20Q/ref=oh_aui_search_asin_title?ie=UTF8&psc=1
I have absolutely no idea why this occurs every few months. Sometimes it last for a few hours and sometimes a few days. Currently it has been here since yesterday. I have tried switching the port I have it plugged into. I made sure everything is fully connected. I have turned it off and unplugged everything and plugged it back in. Pretty much all of the basic things I have tried but nothing worked. Not sure if this helps but only I can see it. If I share my screen or something my friends cant see it. Not too sure if there is a way to fix it but any ideas will be appreciated.