External Display's screen resolution got reduced from 2560 x 1440 to 2048 x 1080

[anjanesh]

My Dell monitor C2722DE normally has 2560 x 1440 screen resolution - but today when I switched on my MBP, the display's screen resolution got changed to 2048 x 1080.

I don't understand how my external display's screen resolution got changed. The only thing I did was connect to my Chromebook to the external display yesterday.

 

[Amethyst1]

What happens when you click "Default for display"? How is the monitor connected to the Mac (DisplayPort or HDMI)?