Step 1: Calm down.
Step 2: Realize that glitches happen.
Step 3: There's really no more steps.
This is a glitch that has happened from time to time in 7.1 to different people at different times. It's happened to me a few times, but as you discovered, hitting HOME then UP or DOWN, then HOME gets you back to the Home Screen and when you go into the channel selection then, the glitch is gone.
It's not a pop-up ad. It's a glitch in the display of the menu. Notice that the ad is where it's always been. It's the menu that's not shifting over when the glitch happens.
If you're getting it a lot, then you've getting a streak of bad luck. It doesn't happen often, and when it does, it usually stops after navigating to another Main Menu item then back.
Roku Ultra (4660)
Apple TV (5th gen), TiVo, Android TV (MiBox)
Roku boxes from every generation.
Apple TV (2nd, 3rd, 4th gen)