Isn't it likely that one of such events is engine flameout or some other major failure, so that the 08.19 ping was triggered by some non-normal event on the airplane?
Given there were no other ACARS messages in the preceding 6 hours, it seems a given that the ACARS reporting system was disabled. It seems far more likely that the 08.19 partial handshake was the result of a power interruption (gen offline or similar) resulting in a "I'm here" attempt as the power came back. However, since the message was only "partial" (INMARSAT words) my guess is the power failed again before the transmission was completed.