I have originally posted this in another thread in the Ideas section, but after seeing that some people appear not to experience this while others (including myself do), I think it is more appropriate in this section, so here it comes.
(This is in regards to the iOS app)
I have noticed that after opening the Monzo app for the first time in a session (with which I mean a continuous period of time where the phone is switched on) and closing it (pressing the home button once), it does not ask you to authenticate again when re-opening it.
I am running iOS 11.2.2 on an iPhone 7 Plus, so no FaceID present (as it was suggested in the other thread that the authentication could have happened so fast that we wouldn’t notice).
Also, it seems like all details that were previously visible on the app can be view from the task manager when double-tapping the home button as well, rather then being hidden.
I would suggest changing this.