Unreliable GPS raw logging

I have configured an arducopter 4.0.7 based system with a mrobotics zed-f9 GPS. I have GPS_RAW_LOG=1, GPS_AUTO_CONFIG=1, and GPS_TYPE=2.

The trouble is I usually get GRXS and GRXH in the log file, but not always. Changing nothing between two power cycles I’ll get one with the raw messages and one without. Regardless of the logging of raw messages, the GPS always works just fine.

Is there some sort of race condition here? Why do I sometimes not get the raw logging? Are there some other parameter tweaks that need to happen?