I’m having the same issues.
I tried switching to CAN protocol where I followed THESE instructions. I also did UPDATE of GPS as it was available. But after that I cannot switch back to UART/I2C. It gives me the same error as described above. MissionPlanner reports that it cannot configure GPS settings, and when I try to access it using U-Center I cannot poll any data from GPS (gives time out error) and also cannot update firmware. Looks like HERE2 is bricked.
I tried fixing this issue using using RC3 bootloader and firmware but I when I click to “SLCan Mode CAN1” it just disconnects aircraft from Mission Planner and nothing appears in list. I checked that switch inside HERE2 is switched to CAN, and it is connected to CAN2 port on Pixhawk 2.1.
Any idea how to unbrick HERE2 GNSS Module?