WiFi Hotspot, No Connection to Internet

I have a 2020 GMC Sierra 1500 AT4.  Problem has existed almost since May 2020 since I bought it.  Having worked for GM and managing equipment across the country that requires remote firmware updates, here is what 20+ hours, 6 years and one module/head unit replacement have uncovered:

1) The problem is tied to a weak cell signal when the vehicle is started.  I don't have the best signal outside my house; a recent Verizon wireless booster has fixed that.
2) The vehicle fails to switch to a 'good' cell tower when in range.  The vehicle can be pinged, can receive updates and ~75% of the time still has OnStar access.  As others mentioned, internal connectivity is not the issue.
3) A hard reboot of the vehicle - ignition off, door open and closed and car off for a few minutes allows for a fresh 'grab' of the signal.  Shorter durations, where the green OnStar light goes off in less than a minute and powers down the module, do not work.
4) GM shifted to a Google-based platform for later vehicles, but the problem persists according to multiple posts.  I see a lot of notes about the 2025 updates with issues quoted; I guess it could be worse for me!
5) As noted elsewhere, GM just doesn't return calls - even when you TELL them that they don't return calls, they promise to send to a supervisor, and... crickets.  Most of the time.  Until I engaged GM Engineering directly - more on that later - it didn't happen, promises be damned.  Why?  Here's why...
6) GM's philosophy has been, "it's not happening, so we can't do anything" - and closing tickets is their solution.  Today, I had to fight for 10 minutes after the rep's "updates" - which, after pressing her, were simply going down a checklist - to keep the ticket open and escalate. I referenced the 10+ tickets, dozens of hours on the phone and dealership service time to finally get this.  I was promised a call from a supervisor within 24 hours, but then again, I told me to call between 9am and 11am tomorrow... and called me at 6:15pm today.  And when I asked her to read the notes, she saw 'between 9 and 11' (note time zone was not attached, which I specifically mentioned to the phone rep) and clearly had no clue that she was calling when I wasn't typically available. 
7) A POSSIBLE BAND-AID - but not a long-term solution: Now that I have my cell booster, I didn't think to auto-connect to my house WiFi to make sure I have a good signal.  I'll try that and report back.
8) GM is focused on hardware as the problem.  We have to change that.  Working for a cell phone company many years ago, I learned about the complexity of signal handoffs on our phones, which frankly is downright magic. GM's vehicles use a much simpler architecture - and AT&T's crappy LTE network, which weakens when the wind blows (OK, an exaggeration, but you get the point). 
9) GM Team - my ticket # is 1000001212.  Hope you're listening, and let's get an AT&T engineer involved to help you fix the onboard software problem.  You just got destroyed over selling customer data and owe millions because you, well, lied.  Stop taking the process-driven, TTC (you know what that means, OnStar folks) reductions and blame on the cell signal.  Take ownership and trumpet how you take feedback from owners and develop solutions to REAL problems.  Like when a truck/SUV full of kids doesn't have internet to their devices and we have to hear, :"stop touching ME!" (nod to Bill Cosby) instead of peace.
10) For the love of God, don't respond to this note with a similar message to what you've sent to others in this thread.  Be human, READ - and don't REACT - until you take in what I've read.  If you tell me to email one of your addresses you listed in this thread, my head will explode.  I'll test anything you want, have 2 GM SUVs/trucks, I'm about to replace those 2 and add a 3rd for my soon-to-be 16YO son (ARGH! - that's $250K easily) and have spent $12K+ in repairs/maintenance on my Sierra and the wife's Acadia Denali.  Did I mention I want to replace my truck with a 2026 AT4X AEV when it's released?  For someone that has taken my vehicles exclusively for the last 10+ years, I'm 100% behind you.

P.S. - GM Engineers: I currently have to deal with over 130 config keys for EV charging station equipment, firmware updates for remotely managed software across the US and spent 20+ years in the tech industry (in addition to several at a cell phone carrier).  I'm on your side, but you have to be on mine.  Let me, and many, many others like me, help with the solution.  Hopefully, the clarity, specificity and next steps outlined reinforce that.

I've been having the same issue with the Hotspot for the past month or two. You can toggle the switch over but you must be able to get online - like with your cellular network and NOT the car's network. It's not working regardless - and I DID all the dumb crap to "reset" everything and it doesn't work. Not to mention that no one ever answers the OnStar button no matter what time of the day, you usually have to call the 800 number to get an answer. I don't know but it should be as simple as sending a refresh signal from "base/onstar/att" and I think I found how to do it once but now it's like an Easter egg and lost in the ether. Ugh.... 

When I try visiting the NBI appointment site using my hotspot, I get a "No internet" message—even though I'm connected. Is the site blocking access from hotspot networks? 

Has anyone found a solution to this? I am having the same issue with my 2020 sierra. Sometimes it works other times it does

@yaagbo I guess they just called ATT and told them to enable hotspot for this account. OnStar is a service around ATT data plan and like every cell data plan hotspot should be enabled to get WiFi working . I told them this theory and in a few days they called me and said that I can try again. It worked. They neither deny or confirm that it what hotspot ATT issue.
Well one downside was that I was promised to pay 15$ per month by OnStar agent who got me enrolled and it should be like forever but now I am paying like 30$ or 45$ do not recall exactly. not sure  it is connected to enabling WiFi but it happened.

@simplebro, what did they do to resolve the issue?

It was fixed for me. Appreciate help from OnStar support that called me and got issue resolved.

I have the same exact issue 2021 Chevy suburban I cannot turn the WiFi on 3 months after I got the car call OnStar they tell me the same exact thing as everyone else open the door turn the car off turn the car on after it’s been off 5 minutes what lawyers are we hiring for this class action lawsuit 

Chevy Colorado ZR2 2024 the same problem. Hotspot data sharing permanently disabled in settings. Breach of contract as I was promised to get up to 8 users being able to connect. None can. Even my own phone gets no internet when connecting to WiFi. CarPlay works but uses phone internet not vehicle one. Apps work using Onstar internet however as I said nobody can connect to hotspot.

I am having the same issue. Has anyone found a solution?