It's a bad modem. It does happen out there, not 100% are perfect. I've had this happen on multiple occasions. Stop racking your brain and just swap the modem out...save you at least 2 hours at the job site
... There's no mystery, no mystique....just a bad modem.
It was then that Caroline remembered her kitchen back in Montana, with a stove that she might or might not have turned off, and so with a heavy sigh, she put down the penguin.