Android user here - there are two things that I feel could be improved around the Fingerprint lock:
1) Timeout for the lock - I used YNAB so sometimes switch between YNAB and Monzo whilst I am logging transactions. It gets a bit cumbersome to keep having to unlock Monzo with the fingerprint, even though I may only have been away from the app for around 10-20 seconds. It would be nice to have the option to set a period of time where the app stays unlocked before requesting a fingerprint again.
2) Backup unlock method - Sometimes I find that the fingerprint sensor on my phone doesn’t work too good if I’ve just have had a shower. I encountered an issue this morning where I wanted to check my account but it took 5-6 attempts. A backup unlock option like some sort of PIN or password would be useful.