In version 6.5.3 of 1Password for Android, there is a major security flaw in the new vault locking animation that plays when opening the app after it has been swiped away, the screen locked, or any other action that closes the app's view. When opening the app again after the initial close, which puts the app back into the locked state requiring a pin, an animation plays of the lock closing - the problem is, your sensitive passwords and logins are displayed in the background! If you happened to have a password open with the password revealed, even that password will be displayed for the half second or so it takes the animation to play. It appears to show exactly whatever screen you last left the app from, regardless of how sensitive the content there was.
I will say that my phone's operating system is rather non-standard (I'm running a ROM designed for the LG G4 on my G3 that's a custom tweak), but I don't think this should have anything to do with how the app resumes, and I've had no other issues with the software.
1Password Version: 6.5.3
Extension Version: Not Provided
OS Version: Android 6.0
Sync Type: Dropbox