Just had this om my phone under MDM, post update started getting emails that it was not compliant. Attempted to correct the issue in question ( the pin code wasn't long enough) needed to be 6 digits, was 6 digits but intune didn't believe me or the device. tried to change the digits to 7 but intune could see no change.
Turns out that if you follow the correction path indicated by intune, it will not apply the change. You have to change your Pin or password via the phones normal security setting path. A trap that is easy to fall into as most other MS stuff has short cuts that work.
Hope that helps