Let me preface the following with me being aware that it is a rare edge case.
While opening 1Password today I got a push notification (alert style, to be precise: it was a "xyz is now using iMessage/FaceTime" notification). After acknowledging this notification it led to me being able to unlock the app with Touch ID, and seeing it open in the background, while still also seeing the alert that I should put my finger down for Touch ID authentication. It also had the grey overlay. Pushing the home button or any button on the Touch ID alert didn't do anything. Turning my phone off and on (not a reboot, just hitting the power button) resolved this issue.
I'm on an iPhone 5s with 1Password 5.3 (503007).