Screen orientation on 8 Plus stuck and won't automatically vary between vertical and horizontal

Today, I was working on some videos shot yesterday with Filmic Pro and my iPhone screen began sticking in vertical mode and would no longer go to horizontal mode. The issue began when I altered the "Lock Orientation" mode in the Filmic Pro settings. I was unable to get it to work normally, so to make sure it was not something app related, I saved my videos in Filmic Pro and then deleted the Filmic Pro app off my phone entirely.

Next, and with Filmic Pro no longer installed on my phone, I went to the Photos app and tested some of the photos and videos there to see if the automatic vertical / horizontal orientation was working, and to my frustration, it wasn't working normally there either.

The phone seems to be stuck in vertical screen orientation mode. Does anyone have any suggestion as to what might be causing this? This issue just started this morning and I have not changed anything in the phone Settings.