iPhone X
iOS 11.1.2
Monzo current account 1.9.19
- Freezing card works ok but unfreezing card crashes the app
- Clicking on Settings never quite makes it to the settings screen, …just see a little blue dot running around a grey circle
Around what time were you having these issues and was the app fully crashing or just not responding?
I ask because the timing is consistent with an issue we had tonight where the API that the app uses became slow or unavailable. 
App fully crashed out. Closed down when unfreezing card.
Super slow and going nowhere when trying to get to settings.
Just tried again and all working fine now.
Monzo app just crashed for me when opening from notification.
iOS
iPhone 6