When you changed, did you reset your speakers and then set them up on the new network?

I sure tried...

Sounds like after the speaker reset you created two systems. Rather than adding all bar the first to existing system you’ve created a second system and added some speakers to that. 
 

Reset (again) those on the second system and then add them to existing system. 

I have unplugged everything except the arc…and unplugged the tv from the arc…uninstalled the sonos app from my android cell phone…. Did the same for my iPad and only reinstalled the app on the iPad…I unplugged the other free internet service I get….sonos  app will locate the arc… accept it….ask if I would like to add more products…I select done…. Then … the sonos app no longer recognizes the arc and I have to start the process all over again…

Using the sonos web app… I was able to connect the ones with my arc…. But doesn’t recognize my 2 gen 3 subs…

@Applesauce 451

Personally, I’m not a fan of Mobile internet vs my Fixed land-based ISP due to throttling that can occur during heavy Mobile use periods.  That’s not say that throttling doesn’t occurs with land-based ISP’s; but it’s much less prevalent than it was several years ago.

Today with gigabit Internet speeds being offered by land-based ISP’s if throttling does occur it’s barely noticeable in most use cases. Customers at the far end of an ISP’s trunk-line may have a different opinion. This link provides the data for average Download vs Upload  speeds shown below (YMMV):

Download Mobile vs Fixed

• 50 Mbps vs 91.93 Mbps

Upload Mobile vs Fixed

• 11.3 Mbps vs 43.4 Mbps

The above is not to say that T-Mobile Internet will not work with Sonos; as I will provide some tips to help with your situation. In case you want more independent research about T-Mobile 5G Internet (in addition to your own) click the link for a CNET review updated as of June, 2024.

T-Mobile 5G Internet Overview

• https://www.cnet.com/home/internet/t-mobile-5g-home-internet-review/

The link that follows is to the T-Mobile Community that details how to successfully get Sonos to work with T-Mobile 5G Internet service. I hope it helps resolve your issue to get everything working in sync.

How to get Sonos to work with T-Mobile 5G Internet

• https://community.t-mobile.com/gateways-and-devices-37/how-i-got-my-sonos-products-to-work-on-my-t-mobile-home-wireless-internet-service-52108?tid=52108&fid=37

Let me ask this… on my arc and on my 2 subs…I see what looks like Ethernet connections…. If that is the case…. Can I connect the subs by running Ethernet cables from the subs to the arc ? …and leave it that way?  ( the five minutes ago sonos app update for iPad and android didn’t allow me to connect.) 

the app does recognize the subs— just tries and fails to connect them … 

In theory yes for one sub. However, a splitter would be required for Two subs and I’m not sure if that’s possible.

Didn’t seem to work…. Watched some unhelpful YouTube videos…. But…. T mobile internet app is set for for automatic as to 2.4 or 5 Ghs….wpa2/wpa3 as opposed to. Wpa2/wpa2 or wpa2. With AES WPA encryption mode.. whatever those are….

I only use the internet for one room…. So…should I change any of these settings? 
 

my system is  2 gen 3 subs… 2 ones and an arc… all less than 2 years old… thanks…

The extent of my knowledge is only what I presented in my initiail response. The best I could offer is the link to the T-Mobile community detailing how to use Sonos with T-Mobile Internet. 

However, regarding setting their box to auto 2.4Ghz or 5Ghz (I'm assuming you mean as default) if those are the choices I’d go with 2.4Ghz as it has the best range. Once the Arc is setup it will use its own proprietary 5Ghz band tp communicate with subs and/or surrounds.

In case this might help @Applesauce 451; forgive me if it’s been mentioned as I haven’t read this thread through.

I recently switched to T Mobile “cell” internet (which bangs), with the, new, white gateway.

Loooooooooong story later... I could not get the Arc, sub3 and OneSL pair to connect. Finally, I connected a OneSL via ethernet to the main, switched network (automatically picks, 2.4 or 5), with WPA3. It took a few hours, but finally, after several factory resets of all speakers the system connected.

Just upgraded to a pair of Era 300s. Same thing, a few hours of going around in circles (having tried Sonos support in 2021, when I became a customer, I knew better than to call in.)

I was surprised to see the ERAs did not have ethernet port, as I was planning just connecting one of the pair as I did the OneSLs, and leaving it, as I did with the OneSLs. I now see I could probably have disconnected ethernet’d OneSL, but didn’t want to chance it, having put in so much time setting up the darn system, lol.

After an hour of futzing around, and several factory resets of all speakers, I connected the Arc via ethernet to the switched network (automatically picks, 2.4 or 5), with WPA3. I did not use the 2.4 and 5 individual networks I had created.

It all finally connected, but because the Arc in not near my gateway, I disconnected the ethernet cord after my TV session last night, fully expecting to have to start all over today, probably moving the gateway to be near the Arc.

To my surprise, the ethernet’d network, was now all wifi, and everything is connected with full functionality and this happened automatically, after having disconnected the ethernet cord last night (Again, I now understand the ethernet’s aid in initially setting up the network, which will then function via wifi, subsequently).

I love this Sonos system. However, I will never buy any subsequent Sonos products.

It’s not just Sonos - I am finding too many companies, in all kinds of different verticals cannot service their varied product lines, and the scale of how many customers they have.

K-sera, I’m over getting angry about it. It’s clearly time, for sanity’s sake, to start living with less tech, less products, less interactions with large corporations, less everything and to focus on becoming as self sufficient  as possible with the services and systems that are important to one, regardless of one’s income.

My hope for us all, is the ship continues to sink slowly, and does not capsize...

I gave up and went back to my old internet provider…. I suspect Sonos will eventually get it together…. Sigh…. Thank you for the info though….

We gotta’ be self sufficient and make it work, with the resources we have and can find,’Sauce.

Sonos will not get it together, you know why? 

1. The individual networking setups, in each customers home, present exponential variables. They can’t service this technically; only chip at percentages. 
2. Resource allocation and net/net operational profitability and shareholder value; no company is going to spend to service their customers; hence, phone trees designed to eat up time, constantly trying to vector you to chat, bots, texts etc. It’s just that simple.

My 3 year experience with Sonos CX backs this up. I remember my first call back in fall of 2001, the person was so incompetent, I hung up and never called back.

I don’t care what Patrick says; he knows I speak the truth.

This is not just Sonos, it’s almost every large corporate entity I deal with from Lemonade Insurance, to Blue Shield Ca., to AliExpress, to et al. ad-infinitum. Contemporary corporate entities cannot, effectively, service the scale they have created.PERIOD.

Amazon is about the only large corporate entity that can service their customers. But then, the $100K I invested in 2020 or 2021 hasn’t moved an inch, lol.

LessTechDigitalMinimalism, less everything. It’s all gotten complicated beyond the ability of the systems in place to manage same. I’m actually not a cynic or nihilist, but let’s talk about what really is and not live in spinLandIsReality.

I have arc, sub gen 3 , 2 One SLs ( Home Theater System) bought less than 1 year ago. Everything great until I changed my ISP from AT&T to Spectrum. Have 25+ smarthome devices moved seamlessly to New Network except One which is Sonos. I myself consider techy.

Past 2 days I'm struggling to move system to new network with all permutations and combinations from these community forums and Not so great you tube videos.

And I'm afraid to contact customer support ad they might eat away our time with no solution.

Why its so hard to move products from one network to other.  Even tried factory reset . I didn't expected this after spending thousand of Dollars.

As these corporations grew larger and larger , cust service going down and down.

I still can't believe my issue is big  and hope Sonos tech improves.

As a techy, you probably realise you’ve not given a lot of detail of what you’ve tried, if you’re asking for help? Or what the symptoms or error messages are. 
As a techy, you probably also recognise that the data packets and reliability demands of a system sending a continuous and sequenced data stream are much greater than, say, a computer sending a file to a printer.