I’ve noticed, since I updated to iOS 12 (I’m running 12.1), that the mail app doesn’t work as fast loading emails and sometimes I can delete an email, close the app, then come back to the app and that same email be in my inbox. I have also noticed before that I can read an email exit the app then come back to the app and that email be marked as new. This happens on my iPad and iPhone, so I’m not sure if it is my WiFi or is it something anyone else experiences with iOS 12? I don’t recall having these issues with iOS 11, but it surprises me how slow the app is at loading emails. This makes me think it’s my internet connection, but the other things I’m not sure about.