I see.
I managed to connect the to the second GPS using ublox u-center and a UART-USB conversor. In u-center the baud rate is initialed listed as 9600 which I found it odd since I was using 38400 in the SERIAL4_BAUD parameter. Nevertheless I manage to change it to 57600, however once I connect to mission planner it says on the "messages"tab that the detected baud rate is 115200 (which also happened in one of your images). Do you know what is happening?
Apart from this minor inconsistence the external GPS appears to be working fine and I was able to fly the drone in loiter mode without much issue. On other hand the internal GPS of NAVIO2 still appears to have some problems, since I keep getting the “Unhealthy GPS Signal” if it is active.