Are the devices that are not able to see it older than the ones that can see it? There are several different frequency ranges that routers can broadcast and older devices (phones, PCs, consoles) may not be able to "see" frequencies that were implemented after they were made.
For example I have a router that broadcasts both a 2.4Ghz SSID(named Tom) and a 5Ghz SSID(named Jerry). My iPhone and iPad that are new can "see" both Tom and Jerry in the wifi connection settings but my PC that is around 4 years old can only see "Tom".
In your case I'm wondering if perhaps the owner changed the router to only broadcast 5Ghz or for some reason the 2.4Ghz mode has accidentally been turned off or is failing for some reason.