I am on the current account. It is currently showing the pop-up warning me to carry an additional card due to planned maintenance on the prepaid card.
As an aside, if I click on “Known issues” within the CA app, they are all to do with the prepaid card.
Interesting. I don’t have one?
Android or iOS?
Android (not pop up, ugly mustard bar across bottom of screen)
Hmm. Looks like a bug.
Suggest this gets merged into: Planned prepaid maintenance early Sunday morning. Please carry another card 💳
Nothing here but there is a planned maintence for Prepaid just got text.
Check here;
https://mondo.statuspage.io/
CA is here: https://monzo.statuspage.io/
nothing for me on iPhone CA
A fix is on the way, next version I believe 
@crablab I’m going to leave this here - as it is a bug report.