Mission Planner 1.3.56 - Waypoint altitude checkbox (relative, absolute, terrain) disappears

Ground Control Software Mission Planner
1

I wonder why randomly the checkbox to define the waypoint altitude type disappers while connecting to pixhawk. Sometimes the checkbox is visible and the type can be chosen, sometimes it disappears:

Some help would be much appreciated!

Mission Planner 1.3.56 (latest stable)
AC 3.4.4
Wint 10 Tablet (Trekstor Surftab)

2

it is removed because the firmware you are using does not support it. please upgrade.