1 device not applying Profile - iOS
Is the problematic phone exactly the same model and same firmware version+build number as the other 9 phones that work? Are they in the same mode (all supervised or all non-supervised)? Do they have the same device agent?
Have you checked on your web console to confirm that the profile with the authentication payload has been successfully deployed to this problematic phone?
Exact same all are 7s with 12.1.4
profile has been successfully as of 1130 yesterday. Then today we change the profile to require a more complex password. All phones updated as did the problematic phone.
I am finding these issues are intermittent. Some phones will receive the profile or not at all and they will display other symptoms, some phones have to enter the ad, other ones need to update the AD as well as the apple id, i do notice now that we are not using a special character in our password when the password required prompt comes up it only provides a numeric keyboard.
If everything (hardware, firmware, agent, modes, etc) are exactly the same, the only difference may probably be the password complexity (none, simple PIN, complex password, etc.) before the latest authentication profile is deployed to the devices. Maybe you can revoke the authentication profile first from the devices, and set the same complexity and deploy the profile, and see if they behave differently.
Finally, please note that MDM related codes are actually implemented by Apple firmware for all iOS devices, and EMM software only passes desired modes/parameters to the device firmware in XML file format defined by Apple. So, if any implementation is really buggy, the problem can only be solved by Apple.