Same issue here on the latest iOS. Monzo makes my phone restart itself randomly then when it comes back the app won’t open. It just closes immediately so I need to delete it, restart again then download it and set up my account all over again. This usually works for a few hours but I find that I need to reinstall monzo at least 3-4 times PER DAY. It’s bad enough the app does this but it also restarts my phone (analytics reports all point to monzo being the issue)