I signed up for fibre broadband with vodafone and was given two identifiers, one with a -5 after it. It was supposed to be faster. Recently, it ceased to be possible to join it, and now it has disappeared as an option altogether. Why is that?
Which modem? The HG659 or the newer grey Ultra Hub?
As a guess you are either too far away from the short range 5G wifi (move closer to test) or the 5Ghz is turned off somehow, or even that your device doesn't support the channel it is using (rare)
Does a modem restart bring it back?
Turning the modem off and on did the trick.