This is me almost every time I interact with ISP support.

Except… recently I completely misdiagnosed something. So while I was getting politely frustrated with the support clerk, he was stepping me through a set of irrelevant seeming procedures which, indeed, resulted in identifying that a piece of hardware was broken.

In this case it was the fiber to Ethernet adapter my ISP uses. He needed me to verify that, at every step of the way, pieces of my infrastructure were not the cause of my flaky connection (they weren’t). However, as a final step he had me reboot the adapter and it didn’t start back up. Turns out this is a rare failure mode and the flaky network I’d been seeing was an early, year long, symptom of this issue.