it looks like AM/PM format not showing after update to v110. zenfone 6
but they says: Added the ability to show AM/PM with 12hr clock-format.
It was fixed after full reset
It could also be that it was disabled in the "notification bar settings" in -> Settings -> Display -> "Status bar icon manager"
A bit late reply now that you reset it anyhow.
I think it was also disabled in notification bar settings. I enabled it in settings after full factory reset.