When you open the Monzo app it can take up to a minute to refresh your timeline (on a good internet connection).
As we become more and more dependant on the app to approve things like online payments or add cards to Apple Pay this is becoming an issue rather than an inconvenience.
Details to reproduce:
Open the Monzo app. Wait for the information on screen to update
OS: iOS 13.1.3
Device: Apple iPhone XS
App Version: 3.4.0
Check this thread out which is already highlighting the improvements coming soon: