Deleted a video. Why does it keep reappearing momentarily?

I deleted a video from my iPhone 6 Plus weeks ago. Sometimes when I use the camera function on my phone without unlocking it, I'll see a glimpse of the video that I know has been deleted from my phone. It sometimes happens when I go into the photos app as well. Almost whenever the phone is unlocked mostly and I try and access my photos. Why does this happen? Is this a known issue?