thin line across screen appeared but then disappeared?

Earlier this morning, when I turned on my iPad, I noticed I had a very thin pixelated line across my screen display. The line was not there yesterday, which was also when I was applying my screen protector, if that is a factor. The iPad is a refurbished from Amazon, which only arrived 4 days ago.

Upon research, I saw a lot of posts about the same exact issue. I tried restarting twice this morning, but to no avail.

However, a few hours later, the line disappeared on its own. The only things that occurred since then were, a systems download+ update+ restart, a couple hours of painting in Procreate, changing my wallpaper for both home and locked screen, and charging the iPad. It’s been around 10 hours since and the line hasn’t appeared back (yet). I even restarted once more to see if the line would come back, but things are still normal.

My question is, will the line come back or are things back to normal, to where I don’t need to get a replacement?