Couldn't find a formal bug reporting location, so posting here. The 1Password iOS application would not let me log in to the app, as it said I had the incorrect master password repeatedly, however, I was entering the correct password as I could successfully log in on the desktop application.
I was able to solve this by uninstalling and reinstalling the application.
1Password Version: 7.2.5
Extension Version: Not Provided
OS Version: iOS 12.1.1
Sync Type: Not Provided