I looked at the PX4 documentation on LEDs and online at Holybro’s website and there doesn’t seem to be specific LED layout for the Holybro Pixhawk 4 2nd GPS module.
I found this tidbit on the LED meanings page which could provide insight to a potential solution, " It is possible to have a GPS lock (Green LED) and still not be able to arm the vehicle because PX4 has not yet passed preflight checks. E.g. A valid global position estimate is required to takeoff!
You can access the preflight checklist by left clicking on the purple QGroundControl icon in the top left hand side and selecting Application Settings. Under the Application Settings page the very first option at the top under the category Fly View is a checkbox for a preflight checklist. Once you check the box by clicking it then there will be a new Checklist option under the Fly menu bar in the top left of the screen. Hopefully this helps you solve the problem. And if anyone on the dev team sees this, I think that this should be a default option since it improves operator situational awareness and can prevent arming.
I’d contact Holybro and see if they have anymore info on the GPS module meanings if the preflight checklist doesn’t help.