Display won't turn off automatically even when it is set to do it

Hi, I have my settings set to turn the display off after 10 mins and it used to work but recently started just not paying attention to that setting at all - screen stays on always unless on battery power. I tried playing around with "Prevent your Mac from automatically sleeping when the display is off" (both enabled and disabled) and changing the timing on the display timer to no avail. Screen stays on all the time regardless. How can I fix it so it respects the timer and turns off the display?