Granted its an article from the sun but it has some interesting details. With 60 closures a week being reported to the Ombudsman you can learn what your rights are and aparantly…
Which should be good news for Monzo and their Trustpilot page.
Wonder why so many are being closed. 
So it was an average of 50 a week in 2018 versus the first few weeks of 2019 where it has been an average of 60… not sure that’s a great start to the article, comparing 52 weeks to 5 
Typical click bait from The Sun, not that I’d expect anything less. My honest guess is AML and KYC, but I could be wrong. If it’s AML the bank has no obligation to tell you anyway as this will tip you off for other accounts you may have.
Ultimately, always make sure you have at least two accounts so that if one does get closed you already have a second. If it’s closed due to fraud/AML then you may well be without an account at any bank.
This is just happened to me with nationwide, thank you for this article I shall now be complaining to the ombudsman because my account was neither been used for fraud or anything it was just dormant and they didn’t want to pay for it anymore.
Sounds to me like they were just trying to help. You clearly didn’t use the account and it’s usually a complete hassle to close anything high street.