SD-PMUs showing offline in InControl2 and Access Error: Unexpected end of file from server?

We have two SD-PMUs on our boat and they are showing offline in the InControl2 device list for the boat.

We can access the SD-PMUs via the InTouch button from the Max HD2 MBX Router, but on one unit, when we access the settings, we receive the error message Access Error: Unexpected end of file from server and then we can no longer log into the devices.

Thanks in advance for any ideas