I had that happen to an app on my phone once. It was strange. I had to reboot the phone, it came back after that. Never figure out what caused that.

I started on the 6s in 2015. When the XR came out, I got one and tried it for a month. I liked the battery life, but I couldn’t get Face ID to work well for me. It also probably didn’t help that I was so use to a home button. So, I gave the XR to my daughter and I went back the the 6s, which is still being used today.