Look at the GPA2.DELTA or GPA.DELTA (depending on where you have your GPS connected) from your dataflash .bin file in the log viewer in Mission Planner. The value should be around 200 mSecs. You will have Bad GPS Signal Health if you have values greater than that. The term “GPS Signal” is referring the the timeliness of the signal from the GPS to the flight controller, NOT the signal the GPS is receiving from satellites.
I received help on this same issue about a year ago from much more experienced users than me. You might skim through the discussion around here: Bad GPS Health when I have RTK Fix.