It should work with 5Ghz just fine, but 5Ghz is more subject to wifi interference than 2.4Ghz, due to the radio frequencies involved. For instance, it can get absorbed by walls much more easily. Read that FAQ I linked to, take a look around your speakers for possible sources of difficulty. And be aware that all sources may not be within your network, or even your house. In Texas, I had a new neighbor next door who set up their router on the same channel I had been using, which caused issues for my network. 

5G internet or 5Ghz wifi? 5G internet (so via a mobile network instead of a landline) is not supported by Sonos. 5Ghz wifi only on certain Sonos devices.

So did the Support Staff mention that this is because there is an SSDP Multicast ‘Device Discovery’ issue between your routers network segments when the controller device is on a different band to your Sonos speakers? If so, then did you try a wired SonosNet setup to see if that would resolve your issue? 

You need to give a bit more detail about the reasons of what was said and what you’ve tried so far. It would be helpful to know what the network setup is, including make/model of router and any other access points, switches etc. otherwise it’s slightly difficult to make any suggestions here for you to perhaps try.

Sorry, I should have mentioned that I don't have a problem with Sonos music/radio, no connection issue there,it's when I try to  use spotify or Apple Music. The router was checked and it's fine.

So what is/was the issue mentioned by Sonos Support precisely, as those services are all lossy services, so presumably it’s not a bandwidth issue - the 2.4Ghz band is more penetrating than the 5Ghz band, but slower…if using WiFi what were/are the SNR levels of your speakers. See this Support Link as that will help you discover their current SNR levels…

https://support.sonos.com/en-us/article/understanding-the-network-details-section-in-the-sonos-app

One speaker is 49 db and the other is 60. Both show excellent connection. At this moment spotify is working. After an hour conversation,yesterday, the sonos tech suggested to change my internet  from 5g to 2.4.  Said as long as I had 5g I will experience inconsistency in connection

The strength of the signal, at the moment, sounds fine - if you have the 2.4Ghz/5Ghz WiFi bands broadcasting separately by your router (with different SSID’s) then you can set your Sonos products to just use the 2.4Ghz band only if you want, then everything else compatible with 5Ghz around your Home (and in range) can use the 5Ghz band. That perhaps might assist, but if you do that, then I would set the 2.4Ghz band to use a ‘fixed’ non-overlapping channel of either 1, 6 or 11, with a channel-width of 20Mhz only and see if that perhaps sorts things for you. Just leave the 5Ghz band with a different SSID name and a channel-width of 20/40/80Mhz.

Hope that assists.

Appreciate it,thanks