S21 ultra Signal loss problem after uploading to one ui 7

[Ahmadi]

After updating my S21 Ultra to one ui 7 android 15 , I have a problem with the network connection.

The network is completely disconnecting and goes into emergency mode, or it loses the antenna altogether, and I need to restart my phone every time to be able to connect to the network again. 

[Spencerk]

Yep, after this HORRENDOUS fkin update, I've gone from 4 bars to 1, everything is buffering I'm getting DNS errors and latency with pictures not loading. I can't even listen to YouTube while I'm driving anymore. No problems before this buggy, ugly, update. 

This update has litterally destroyed my phone.  I was going to upgrade, but nope. I'm done with Samsung, they are a fkin joke of a company. 

[MaximConan7564]

Everybody is reporting the same problem on all internet forums. My own A55 just became useless yesterday (27th June 2025) after One UI 7 upgrade. How did they dare change the signal power when doing a UI upgrade? And how are they unable to restore it to normal power? Do Samsung hire only junior part time programmers? 

The funniest part is they answer "bring your phone to authorized dealer for antenna repair". What a joke. They mean yesterday the antenna was ok, but upgrading to UI 7 broke the antenna? Modern software has strange physical capabilities nowadays...

[chief455]

S23 5G here.

Wifi from my home modem was working just fine until ONE UI 7 update. 

Immediately my phone will go from connected to modem-> dropped, running off mobile data and searching for wifi-> sometimes reconnecting to my modem, sometimes I have to go to Settings/wifi/ connect, and I have wifi again. 

Within minutes, the phone drops connection to modem again  -> repeat. 

I have reset network settings, rebooted the modem, their is not available update ( says my software is up to latest version)

It's the ONE UI 7 software!!

My phone and home modem didn't suddenly change intricacies. 

I'm not a Samsung tech, I'm not getting paid to work for hours trying to correct something Samsungs software update disrupted. Samsung  - allow update resets!! It's MY PHONE,  NOT YOURS!!

Give me back ONE UI 6 - at least the wifi was stable. 

This is continuation of update failures and needless changes to MY PHONE. 

I don't want 6 new games installed with every update either. 

Fix this software update, or reverse it until it's sorted.

[osgooden]

I no longer have lte only 4g 

[Members_xf5BJ8L]

Hello,

After updating my Galaxy S21 Ultra (T-Mobile US, prepaid plan) to One UI 7 (Android 15) I started experiencing constant network issues:

The phone frequently shows “Emergency calls only” or “Searching”.

This happens in locations where coverage was always strong before.

Even when Wi-Fi Calling is enabled, the phone loses registration and calls/texts are unavailable until I restart the device.

Important note:
My wife has the same Galaxy S21 Ultra on T-Mobile, and she noticed the problem first on her device. Later I also started experiencing the same symptoms. This suggests the issue is not isolated to one phone or SIM, but may be related to the recent update.

Steps already taken:

Converted physical SIM → eSIM (T-Mobile). No improvement, the issue remains.

Reset network settings.

Summary:
The problem clearly worsened after the One UI 7 update. Since switching to eSIM did not help and the same issue appears on two different S21 Ultra devices, this looks related to modem firmware/software rather than the SIM card.

Could Samsung please confirm if this is a known bug with the S21 Ultra modem firmware on One UI 7? Is there any upcoming patch addressing this?

[uservgC0w0xmaJ]

No, no fix, as satanic Samsung simply wants to brick the phone so you buy another. The issue is with the software, and it's planned obsolescence. In other words, if you are intelligent, stay purely away from Samsung as a company.

[user77OHZgm3x5]

When making a call today I get the message "Your phone's not registered on a network so you can only make emergency calls."

I checked and there are no network outages in my area.

[Mujibar]

That would be a carrier issue, not a Samsung issue.

[realaud]

Do you have a physical SIM or an eSIM?  If you have a physical SIM, take it out and reseat it.  If it's an e-SIM, it's definitely a carrier issue. You have an S21, it is also possible your mobile antenna has failed.  Do a diagnostic on the phone and see if anything comes up as other than "good" or "normal".  Diagnostics can be found in your device care settings.

[meself]

Either your plan stopped or your in a bad signal area