Not answering your question but a suggestion instead. Why not wire one or more of your Sonos to your Ethernet and take them off your home WiFi? That lets your Ubiquity gear operate as designed without having to dial the operation back to levels that Sonos requires. It also lets Sonos manage their own networking with no impact on your WiFi setup.

Maybe helping with the question, I abandoned Standard / WiFi mode long ago but from what I remember I had to enable B/G mode on the APs, disable AirTime Fairness, both had to have the same SSID and be on the same 2,4 GHz channel.

I have 7 sonos devices across 2 AC Pros (all wifi) and I do recall a few Unify controller firmwares back (and AP firmwares) having had the same problem. Always the same SSID, both 2.4 and 5Ghz, last 10 months all works flawlessly. In other words, update your Ubiquiti and if not using a controller, do use one (windows or linux are both free, then there is the Key etc)

HI!

Have problem with Sonos devices on Ubiquiti Wi-Fi.

5 One SL’s and Move.
Wi-Fi consist of Ubiquiti Unifi Security Gateway (USG) + 3 AP AC Lite’s

Two of One LS’s and Move do connect via Wi-Fi, updated and lost connection after update.

Only one that I know, that security level oа Wi-Fi is low, by message in iPhone and MacBook.
 

In same time, AMP, connected via Ethernet works fine.

Any advice or guide for Unify setup?

Did you see my post above?  

I don’t have a Move here but I’m really happy with my Sonos on SonosNet (one or more wired) and my other gear running on a fully optimized Ubiquity WiFi link.

If you really want Sonos on Ubiquity provided WiFi dig back and see the posts about what settings had to be changed to get it working well.