Why do links open in browser and not app?

I am having a strange problem that I have been trying to figure out for the last several days.

In the past when we would open a link in our browser, it would open in the app. However, recently, we noticed that all links are opening in the browser and not the app. I've tried clearing the browsing history and re-opening our settings, but nothing is working. We use the same iOS devices (iPhone 5S and iPad Air 2) that we've always used to open links, so I'm assuming that there is something that is different on our phones.

What I've Tried. I've tried: Checking my settings and ensuring that the "Open Links in" is set to "App". Clearing all browsing data. Checking the "Open in" under Safari > Privacy > Accepted Browsing. Rebooting both devices. What else could I do? Try clearing the history and cache in Settings > General > Reset All Content and Settings.