hamster3null,
The SATCOM is powered by Left Main AC and comes on with power established.
The system will reacquire if the aircraft to satellite beam is interrupted or power interrupted. Beam interruption could be due to wing masking (large bank angle), blind spots or terrain. This aircraft is the last of the Malaysian aircraft to be fitted with dual side mounted antenna; this in itself raises some food for thought.
Side mounted systems have fore and aft blind spots (key holes). The satellite connection was lost somewhere between 17:07 and 18:03; apparently the period where some severe altitude changes were to have taken place. The course from around 18:03 to 18:22 is straight and toward the satellite; if climbing in this period, could it simply be the SATCOM is in a drop out condition?? Change direction at 18:25 and system reacquires.
Alternatively Left AC was turned off and re-established at 18:25.
My guess is a drop out condition.