That conflicts with the setting DisplayUnit = 1440.
When DisplayUnit = 1440, that means the duration of a timeslot is 1440 and when you move an item, the resolution of the new timeslot is thus 1440.
there is anyway to workaround this ? using event code ... or other ?
Sorry, this is a core behavior of the Planner for which there is no workaround.
DisplayUnit should match the time resolution you want to use. You can customize the painting of timeslot borders if you do not want to have these smaller timeslots visible.