iPhone group mms message reoccurring problems

This problem of not receiving group MMS messages with iPhone 6s keeps reoccurring usually monthly, It seems no one at AT&T knows why it occurs, or how to fix it.
Below is my conversation with Apple where they clearly say it's a CARRIER issue.

Guia
Thanks for contacting Apple Support. My name is Guia. Please give me a moment to look over your information.

Guia
Hey there, I hope that you’re doing well. Your case number today is ************. In the event that we get disconnected, reference this case number so you can pick up where we left off.

Guia
I am here to help resolve your issue or get you to a path of resolution. Please tell me what you are experiencing including any error messages you may have received.

Me
Ok thanks, my quest is about group messaging that involves both Apple and android devices, I assume the message is sent as a mms message. My question is do those messages go through Apple or are they strictly a carrier message?

Me
I'm asking because Ive noticed I sometimes get a receiving delay, or do not receive any messages at all sometimes,

Guia
It seems that you have questions about how group messaging works. I know we use our phones for absolutely everything, so I can only imagine how concerning this has to be. Let’s work together to see if we can get the information you are wanting.

Guia
If you experience delays, there are a lot of possible reasons. it could be related to your wireless carrier or your device settings.

Me
My device settings are good. It only happens with mms group messaging sometimes. And the fix is using the reset network connections in the settings. I'm trying to figure out if my problem is with Apple or AT&T?

Me
There's countless of forums and message threads online with ppl who have expierenced the same problem. No one knows why tho.

Guia
Do you use iMessage on your iPhone?

Me
So if you can find out if those group mms messages stay on the carrier side only? I'll contact them. I've been told by my carrier before the problem could be with Apple. Yea do use iMessage.

Guia
Actually I can say that both are involve with this issue. There is an on-going research on our end in an effort to resolve this problem. When did you first notice the issue or start experiencing the problem?

Me
I've noticed quite a bit. Is hit or miss when it happens and I'd say it occurs ever three or four weeks.

Guia
Thanks for letting me know. Do you recall a specific event that may have caused the issue?

Me
And usually a week or so after resetting network connections I'll receive an message from unknown sender that says content not found or something like that.

Me
No not really, maybe when we're all texting in the group for a while it'll do it

Me
I've had receiving delays of an hour to a few hours before

Guia
Alright. We can try some troubleshooting to resolve the issue. Do you have an access to a computer with iTunes installed?

Me
AT&T seem to have a good network, I know most ppl with android devices do t usually experience this issue also.

Me
It's not happening now. And I can fix it by deleting all my current group messages and resetting network connections if it does occur.

Me
My phone has all its updates. There's got to be a better way of fixing it when it occurs. Resetting everything makes me have to re enter wifi passwords also

Guia
Alright. In any case the issue will occur, we can try to restore your device using recovery mode. This is a great troubleshooting step for that kind of issue. I can send you a detailed guide on how to do it. In any case you’re not comfortable performing those steps, you can chat back in with your case ID ********using the following link Sounds good?

Me
Not really, no matter what any solution you have to perform on the device itself I've done it already. And even doing it the problem will eventually happen again.

Me
So what your saying is the group mms go through both AT&T and Apple?

Me
I know they go through att no matter what I was not sure about Apple

Guia
If you’re using iMessage, it is a feature of Apple devices, if you send regular SMS or MMS, it will be from your wireless carrier.

Me
It never occurs with iMessage, just group messages that use mms style messaging. So I guess my problem is with AT&T?

Guia
You can get in touch with AT&T for further assistance about this issue.

Me
Ok thanks I will. Glad to hear Apple is also trying to resolve this issue. Thanks for your help.

Guia
You’re welcome, Is there anything else I can help you with?

Me
No that was my only question.

Guia
It’s been my pleasure chatting with you today, If there is nothing more for now, you can go ahead and end the chat. We are here for you via chat 24 hours a day, 7 days a week. Again, my name is Guia and I’ll be sending you an email with our case number once our chat concludes.
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I guess my question is, is switching to Verizon the only permanent fix for this problem? Or is AT&T going to fix it?