Note that turning off wireless on all devices turns off the ability for the surrounds and Sub to communicate across the ‘hidden’ WiFi connection they’re designed to do. You could be adding a slight processing delay by forcing them to go through your router first, before sending the signal to them.

Unless you’re experiencing WiFi interference on any particular device, you really shouldn’t turn off the radio. 

I wouldn’t ‘force’ any device to be on a particular band 2.4Ghz or 5Ghz, let them choose, as they were designed to do so. 

If by ‘older Amp’ you mean a CONNECT:AMP, then yes, it does need to be wired, as does the Arc, as the Sonos CONNECT:AMP was designed, built, and sold without a 5Ghz system that could accept a surround signal. See the setting up Amp or CONNECT:AMP as surround speakers FAQ. If, however, you just have a Sonos Amp, it does have that 5Ghz system, and can be bonded wirelessly to the Arc.

Since you’re running an overly complicated Unifi network, make sure you’ve read the helpful: https://github.com/IngmarStein/unifi-sonos-doc

As I suspect you’ve found, Sonos doesn’t work well across separate VLANs, but as long as everything is on the same one (subnet), you should be OK. I suspect, although there’s no proof yet, why you’re having trouble with AirPlay 2. Although it might be other networking issues, such as duplicate IP address issues, which might include the problems you’re experiencing with the PLAY:3s.

Rather than trying to force Sonos into your own ideas, I’d certainly recommend leaning in to a more general setup, as Sonos was designed for in general use, but that’s just my opinion. 

Thank you for responding. I should’ve been more clear. The Arc is paired with the newer Amp. I also have a separate older amp for outdoor speakers. But both amps are wired.  Every device has a reserved IP address through DHCP. There are no duplicate IP’s.  I see what you’re saying with the sub communicating through my home Wi-Fi, and not Sonos’s built in Wi-Fi. If I reenable Wi-Fi on the arc, should I also leave it plugged into ethernet? Or should I unplug the arc from ethernet?  (I misstated earlier … currently both the arc and amp plug into the wall Ethernet.  Though I could plug the arc into the amp if that would help).

I think I disabled wifi earlier since I had multiple hard wired devices and was getting routing loops or some thing.  Would I be better off to make everything wifi only with no Ethernet plugged in ona y sonos device?

There’s no reason to unplug the Ethernet cable, even when you turn on the radio, as I understand it, the software is designed to handle it. But it shouldn’t matter, either way. Test both, see which works better for your system.

Disabling the radio sounds like an attempt to get around the  RSTP settings that Unifi uses as a default. I’m pretty sure that’s explained in the link I supplied.

I tend to stay away from overly complex networks, I’m not smart enough, nor appropriately trained or cognizant of all the related issues. But I do think you’d be fine with all devices connecting to the single subnet of your WiFi, and nothing wired to the router, since you’re not using your CONNECT:AMP as a surround driver. Then just let each device decide whether it connects to a 2.4Ghz or 5Ghz channel, per the design of the system, and no ‘forcing’ one connection or another. Let the Sonos software do the work. 

As ​@Airgetlam stated you seem to have an overly complicated network. By comparison I have 31 Sonos units all running on my Mesh network consisting of three (3) ASUS ZenWiFi Pro ET12 routers. One router acts as the main node and the other two as satellites. 

All devices you have listed are WiFi capable and incidentally can receive the hidden 5Ghz signal sent by the Arc. *

Circling back to my Mesh network it is a try-band consisting of 2.4Ghz, 5Ghz and 6Ghz bands. All have the same SSID and Password. My Sonos units select the band they want to use (not the 6Ghz of course) and all works perfectly. I can have 64+ products running on WiFi at any time.  I have no issues with Airplay to any of my Sonos units. Below are snippets of my network:

Again as mentioned by ​@Airgetlam I would enable WiFi on all Sonos units. Additionally, I would give each band the same SSID and allow Sonos and other WiFi devices to choose the band they desire. Multiple SSID’s may be the issue with AirPlay .  I wouldn’t wire any products unless absolutely necessary. The Arc can communicate with the Amp using the hidden 5Gz band.

 * Of course the Connect:Amp cannot accept a 5Ghz signal

EDIT: Looks like I mirrored ​@Airgetlam most recent response while I was still typing. 

Great minds, and all that ;)

In addition to the previous posts, your UniFi network may have band steering enabled which tries to ‘steer’ client devices to 5GHz, some older devices may not like this, so your Play 3 may prefer the 2.4, and your AP is trying to get them on 5, they don’t like it so go back to 2.4. repeat. Try disabling this.

Some devices may be roaming between AP’s, especially if they are between AP’s, and/or the APs are SHOUTING, ie radio is set to high.

Check the Unifi management system log, client tab, you only really want to see mobile devices roaming:

I would look at the client list on the UniFi management screen, enable all column's and check RSSI for the Sonos devices and what AP they are connected to.

https://help.ui.com/hc/en-us/articles/221321728-Understanding-and-Implementing-Minimum-RSSI

You may fine reducing the radio power can improve roaming, especially if you have more APs that you need, often, less is more.

DONT change lots of things all at once, make a note of what you changed, test and wait before making further changes.

edit: And also to confirm above recommendations, a single SSID for all bands. In fact try to have the minimum SSIDs as possible, as each SSID will utilize additional management frames:

https://documentation.meraki.com/MR/Wi-Fi_Basics_and_Best_Practices/Multi-SSID_Deployment_Considerations