What happens when no MAG is detected?

Using the Snapdragon Flight and have a system with an internal and external MAG. Also since it is an SD Flight the preflight checks are “bypassed”. I have an issue where sometimes the external MAG is not detected (Bad I2C lines) and then when flown the EKF can’t get a solution. My questions is does PX4 have the logic to switch MAGs if one is not detected on power up? Also, is there an easy way to know which MAG is being used for the flight without the mini-dm output?