Understanding and Troubleshooting Heartbeat messages

Hi,
I was flying a setup in which I was controlling via a Companion Computer in GUIDED mode, and intermittently ran into issues in which the Companion Computer reported that it was not receiving HEARTBEAT messages from the autopilot, for anywhere from 2-8 second gaps. During those periods it continued to receive GLOBAL_POSITION_INT and other messages - it seems like only the HEARTBEAT message was missing. I am trying to debug whether this issue is within the Companion Computer itself and something it is running (probably more likely), or the autopilot, which was running Plane-4.3.7.

My question is, does the autopilot always send out HEARTBEAT messages at ~1 Hz, or are there situations in which it would not send HEARTBEAT messages regularly (but continue sending other messages)? And, is there any way to see from a .tlog or .BIN file of the flight when it was sending HEARTBEAT messages?