It always happens that the alarm does not ring.
The app seems to work normally and also displays the alarm function, but the alarm clock is silent.
I use my Z Pro as an alarm clock and therefore it is annoying when it does not work.
My smartphone is not set to silent.
Some days everything works without problems and on some days the alarm does not work.
So firstly please update your phone (settings - about phone - wireless update) if doesn't see updated please go here and update with OTA zip file as local update. http://community.umidigi.com/forum-150-1.html
The latest one is android 7 but firstly you need use April update and then June (of course if you want)
I'm not baseless at Android 6.0
As long as Android 7 is not stable, I see no reason for an update.
For me Android 6.0 runs well.
Only the camera app and the problem with the alarm clock disturbs me.