A colleague used an app's "generate secure password" feature to change their ISP's web portal login - which then also became the WAN router's password - which they didn't realise.
It was about a week before the router dropped its connection and needed to re-authenticate - and that's when I was called in to investigate the loss of connectivity - which Windows 10 very unhelpfully reported as the network cable disconnected and was resetting or power-saving on the NIC so the "link active" LED on the switch was going out for about 2 secs every 10 sec. Cue a round of cable and switch swapping to no benefit. The LEDs for all other devices on the switch (running Linux and mostly internal servers) were behaving normally.
I finally backtraced to the router and a useful error message. We put two-and-two together and my colleague called up the auto-saved details in their password manager; it was long, and ALL non-alpha numeric characters - starting with a backtick, which the router would not accept. I tethered my phone to my laptop and tried to login to the Web account portal - which would NOT accept the passphrase. I tried it without the backtick "just in case" - nope.
We had to do a "lost password" reset on the portal..and wait for the email with link.
Lessons learned:
The ISP's password change page did not seem to validate input, but the login page did.
Avoid backticks in passwords.
