I seem to recall similar issues where the post date time would display on some devices but not others. I stumbled across a postdetailing how to resolve, unfortunately I can't find it ( to many matches when I search ).
From memory if you go to board settings in user profile, there are 3 settings for date time "My timezone" and "My date format" all 3 fields need to be supplied.
Suspect if not supplied they pick defaults if available from the operating system profile, which would explain it working on some devices and not others.
Update, just found it, see
https://z4-forum.com/forum/viewtopic.php?p=2048677#p2048677