I have just discovered some problems with my wifi on a new 2860ac, and a complication was that I was hiding the main SSID. When I unhid it, it seemed to reconnect, previously the manually setup connection kept failing with authentication errors.
I had used this setup for years with 4 different Draytek Vigors and never had a problem with it. My niece in Spain had a program which "discovered" the passwords for nearby locked routers, so she could connect for free! Hence my hidden SSID (and also a white list, though perhaps overkill. iPhones on the other hand required at one stage that the SSID was not hidden or it would disconnect periodically and couldn't reconnect automatically, chewing up data limit).

sevilla315 wrote: My niece in Spain had a program which "discovered" the passwords for nearby locked

That seems unlikely unless she was brute forcing weak passwords.

It was an app which found the passwords of strangers' routers. I can find out the details if you like. Obviously it wouldn't be legit software as it allows people to steal passwords and freeload in someone's connection.

Right, but it's unlikely that it actually works unless people are using weak or default passwords.
Setting a good password would be more reliable than hiding your SSID IMHO.